This is pretty common in Tyler Perry's movies, because of the fact that he experienced this as a child.
Specific:
8 1/2 Women (by Peter Greenaway): Philip, while mourning his late wife, wakes up in bed with his adult son Storey; from the pillow talk viewers are to understand that something sexual happened between them. The father is horrified; the son is alarmingly eager to rationalize it. After this, the two men fill the house with a group of mistresses, but the Oedipal implications... pale by comparison.
Aguirre, the Wrath of God: Just after his crew is dead Aguirre declares that he'll marry his daughter and found a new 'pure' dynasty. It's evidence of his looming madness ... hopefully, and not something he planned all along.
An American Haunting: It turns out that the "ghost" haunting the house is actually a psychic phenomenon caused unconsciously by the daughter's trauma of being raped by her father. In scenes set in the modern day, the daughter's ghost appears to a mother whose daughter, it turns out in the end, is also being molested by her father.
American Nightmare (1983): While reviewing a series of videotapes, the protagonist Eric Blake is horrified to discover that one of them appears to show his sister Isabelle engaging in sexual acts with his father Hamilton. When he confronts him on the subject, he learns that the affair began shortly after their mother's death. Disgusted, he threatens to publicly expose the affair between them, prompting Hamilton to commit suicide.
Angel Heart: The lead character accidentally sleeps with his own daughter as a result of a years-long plot orchestrated by a manipulative villain.
An Awfully Big Adventure: Alan Rickman's character P.L. O'Hara deflowers his daughter. In all fairness, though, not only did he not know she was his kid, she didn't know it, either, and it's implied that she never found out. O'Hara, on the other hand, did and drowned himself because of it.
Marty McFly has to deal with the romantic attentions of his own '50s-era mother in Back to the Future after unwittingly recreating the events which led her to fall in love with his father. Marty then has to get his mother and father together so that he isn't erased from history before trying to get back home to his own time. It's not actually as bad as it could have been, though when she kisses Marty (much to his horror), she says that it's like kissing her brother (in the novelization, it's instead "kissing my father").
This is referenced and lampooned in Back to the Future Part II's Call-Back scene, when Marty is again woken up by Lorraine — except this time, it's 1985-A, their house is a casino, and she has ridiculously huge breast implants. Onward, to psychotherapy!
Bad Boy Bubby (an Australian film): The film depicts a mother having sex with her simple-minded son who doesn't know any better.
Bill & Ted's Excellent Adventure: Referenced, though it was never pursued beyond a few "Dude, your mom's hot!" "Shut up!" exchanges and Bill eventually telling Sigmund Freud that he has a "slight Oedipal complex". Of course, "mom" was actually a stepmother only a few years older than her stepson, not his birth mother. And, of course, Missy ends up divorcing him and marrying Ted's dad at the start of the sequel Bill & Ted's Bogus Journey, followed by the Big Bad De Nomolos in the closing credits, then by former stepson Deacon (Ted's younger brother) in Bill & Ted Face the Music.
Black Christmas (2006): A flashback sequence reveals that Mrs. Lenz, drunk one night and obsessed with having another child, went up to the attic where her son Billy was kept and raped him. She wound up giving birth to a daughter named Agnes nine months later.
Black Swan: Implied between Nina and her mother. Fan debate rages heavily.
Brimstone: The Reverend is Elizabeth's father, and the reason she ran away from him was because he "married" her against her will following her mother's death. At the end of the movie, he declares his intent to top his previous crime by killing Elizabeth and raping his granddaughter.
Butterfly (starring Pia Zadora): This classic film features an infamous "bath scene" where Jess comes close to having sex with her father Jess as he gives her a massage, but stops just short of it.
Chinatown: Features father/daughter incest in an infamous reveal about Mrs. Evelyn Mulwray and a woman named Katherine who Jake Gittes took to be the mistress of Mulwray's late husband. Katherine turns out to actually be the sister and the daughter of Mrs. Mulwray because Mrs. Mulwray was raped by her father, Noah Cross. Noah crosses the Moral Event Horizon even further when at the end, when, after Mrs. Mulwray is killed, he forcibly takes Katherine, his daughter/granddaughter, into his car, implying he wants to do the exact same thing to her. Evelyn Mulwray was going to be played by Anjelica Huston, John Huston's real-life daughter, as an utterly perverse Casting Gag.
Spoofed in a cutaway on The Cleveland Show, where Cleveland mentions a remake of Chinatown with Miley Cyrus reenacting the famous "She's my sister and my daughter" scene.
Also spoofed in E!'s 100 Shocking Moments In Entertainment Countdown. When they bring up Chinatown, they play the iconic scene between Jake and Evelyn... and then one of the commentators is seen slapping himself and screaming "Mother! Father! Sister! Brother!" several times before he gives his opinions on it.
Clara's Heart: Part of The Reveal about Whoopi Goldberg's character is that she was raped by her son, who then killed himself.
Crimson Peak: Implied as part of Lucille Sharpe's backstory. Lucille drives an ongoing incestuous relationship with her brother, which began before he was twelve and she was fourteen (and she murdered their mother to keep said relationship secret). The novelization also reveals that she had poisoned their abusive father; this fact, coupled with the fact that she initiated a sexual relationship with her pre-teen brother, suggests that Sir John Sharpe may have been molesting her.
The Damned (1969): Helmut Berger's character, Martin, has an unhealthy love/hate relationship with his mother, which culminates with a sex scene that he initiates. Afterward, the mother falls into a catatonic state and is then pushed to commit suicide by her son. Even if it doesn't really qualify as parental incest, Martin is also a paedophile and it is implied that he molests his little cousin.
Dogma: While not specifically stated, it is suggested by the following exchange:
Bartleby: But you, Mr. Whitland, you have more skeletons in your closet than the rest of this assembled party. I cannot even mention them aloud. [whispers something in Whitland's ear]
Loki: You're his father, you sick fuck!
[Whitland starts crying]
Don't Look: Kelley and his daughter Sherri Baby reveal they're in this sort of relationship by making out right in front of the group, much to their shock.
Eve's Bayou: Whether or not a "mild" form of this occurred is the central focus of the film. The theatrical release makes it more explicit that Cisely kissed her father and he stopped her, while the director's cut leaves it ambiguous who initiated the kiss.
Father and Son (directed by Aleksandr Sokurov): Aleksey and his father's relationship is about as uncomfortable as it gets without actually doing the deed. This l includes homoerotic smackdowns and almost-naked caressing.
Faust: Love of the Damned: It turns out that "M" had possessed Jade's father in the past to molest her as a child, in order to indoctrinate her so "M" could later impregnate her as an adult with his demonic spawn. She can only recall traumatic flashes of a faceless man having his way with her.
Forrest Gump: Father/Daughter happens to Forrest's love interest Jenny, not that Forrest understands it. Her dad was "a very loving man, always touching and kissing Jenny and her sisters". When Jenny grows up, she takes it out on her old family home, throwing rocks at it in a heartbreaking scene that ultimately has Forrest have the place bulldozed afterward.
Freddy's Dead: The Final Nightmare: Freddy takes the form of the sexually abusive father of Tracy, and demands that she give him some "honey". He also tries to "convert" his ACTUAL daughter to his side of things, and whether intentional or not on his part he's just as skeevy in his advancements on her. Flashbacks to when he was still alive were deliberately vague in whether he had the same murderous intent with his daughter as with the other kids on Elm Street, or if she was the one exception and he just couldn't help being creepy around her.
The Goddess of 1967: Deidre is the product of this. Perhaps that's why she's blind...
Good Dick: The Woman of the two protagonists turns out to have been a survivor of incest at the hands of her father.
The Grifters: Implied until the end when indeed the mother's lust comes out into the open with tragic results.
Hellraiser: This is hinted at or added subtextually to several of the films:
Hellraiser and Hellbound: Hellraiser II have the lurking phantom of parental incest all over them. "Come to daddy" and all that. There's no evidence that it actually happened, but the idea is pretty firmly put into viewers' heads.
Film/Pinhead: That is the gun you used to kill your parents. Oh, what else could you do? They thought you were so tempting, their affections so conditional.
Hellraiser: Deader: Flashbacks implicate Amy was sexually abused by her father.
Oedipus:(walking around collecting donations) Give to Oedipus! Give to Oedipus! Hey, Josephus! Josephus: Hey, motherfucker!
Hot Fuzz: According to Danny Butterman, Michael "Lurch" Armstrong's mother and sister are one and the same. Implicitly, this is why Lurch is mentally handicapped.
I Stand Alone: The main character (who's nicknamed "The Butcher") has sexual feelings for his mentally handicapped daughter. In the finale the Butcher has sex with his daughter before killing her and himself, this ends up being an imagined scenario and he puts his gun away. However, he makes it clear that he is going to act on his urges, as he believes he is doing her a favor.
Inugami (a Japanese film): The main character eventually discovers that the older woman he's been sleeping with is his mother and that his father was his uncle. It doesn't end well.
Jason Goes to Hell: The Final Friday: An early version revealed that Jason and his mother regularly had sex with each other, with this revelation even having an accompanying flashback of them doing it.
Jupiter Ascending: The several millennia-old Titus Abrasax tries to force Jupiter Jones, the reincarnation of his mother Seraphi, to marry him. However, while he does creepily try to charm her, he only wants to marry her so he can be her heir, then immediately kill her to get the inheritance. On the other hand, his older brother Balem is much more overt about his obsession with Seraphi, which many have interpreted as romantic/sexual in nature.
The Loved Ones: Although Lola and her father have never slept together, it is clear that both want to, Lola being the aggressor in this case. Unlike her, her father at least seems somewhat hesitant, and understandably so.
Machete: Booth admits to Padre in Confessionals that he has feelings for his daughter April, and he's disturbed by this. Later, it is revealed that April and her mother June film Home Porn Movies while he's away, lesbian scenes with each other and/or threesomes.
Malevolent (2002): The killer's backstory involves a sexually abusive mother who was also the Trophy Wife to a wealthy businessman. In addition, she was rumored to have been in a relationship with her own father.
Ma Mère (a French film): Features a very complicated incestuous relationship between a mother and her son.
Murmur of the Heart (a French film): The main character (a 15-year-old) and his mother have a one-night stand. They decide to treasure it and never bring it up again.
Nanny McPhee: Averted but Played for Laughs — midway through the movie, they pass the maid, Evangeline, off as one of Cedric's daughters to trick Great-Aunt Adelaide. At the end of the movie, when Cedric and Evangeline decide to get married, the confused aunt lets out a shocked cry of "Incest!" before they explain the truth.
It's even funnier when you remember Great-Aunt Adelaide is played by Angela Lansbury, who played Mrs. Iselin in the 1962 adaptation of The Manchurian Candidate.
Vicki: I'm going steady, and I French kiss. Audrey: So? Everybody does that. Vicki: Yeah, but Daddy says I'm the best at it.
Natural Born Killers: The main female character is molested by her father. It's played like a sitcom, to make you extra uncomfortable.
Oldboy: The lead character accidentally sleeps with his own daughter as a result of a years-long plot orchestrated by a manipulative villain.
Orphan: The original screenplay used this in Esther/Leena Klammer's Freudian Excuse. She was sexually abused by her father all the way from infancy to adulthood, causing her body to be rendered permanently infertile before she was even out of diapers and for her to spend her entire life believing that sexual relations between fathers and daughters were completely normal.
Pieta: Kang-do, an adult, rapes Mi-sun, who claims to be his mother. Later, she starts giving him handjobs somewhat consensually.
'Let mama make a gift to you! A gift that only a mother can give, a gift so special it will curse this house for years, a gift of supreme motherhood.'
Poor Things actually inverts this trope. Mad Scientist Dr. Godwin Baxter created Bella to be his lover, but his awareness of his own sexual incapability made his unexpected paternal feelings toward his lovely young creation win out, and he ends up a kindly father figure toward her who snuggles with her and reads her bedtime stories without the slightest hint of impropriety.
Precious: Based on the Novel Push by Sapphire: The title character is raped by her father, resulting in two children and HIV. The first child has Down's Syndrome. And it's strongly implied that Precious's mother forces her to "take care of her" (i.e., perform oral sex on her) because she feels that her daughter drove her boyfriend off and, as she says, "Who was gonna love me?"
Psycho: Not stated outright, but the possibility of incest between Norman and his mother is certainly implied.
Psycho IV: The Beginning: This gets a bit more detail: she apparently teased him sexually in his adolescence and then punished him for his natural reactions. As a result, he lusted after his mother and was jealous of her many boyfriends, and assumed the reverse was true, which resulted in a woman being knifed in the shower some 20 years after Mrs. Bates died. It is not clear if they ever consummated this or if he just had one hell of an Oedipus complex.
The Quiet: Elisha Cuthbert's character Nina has an incestuous relationship with her father, who's been molesting Nina for some time when the story starts.
Rebel Without a Cause: Subverted in that the attempts to deny even the appearance of incest destroy the normal expressions of affection. Judy's father refuses to show affection for her, stating that she's "getting too old for that kind of stuff", and when she kisses him, he slaps her.
Romper Stomper (an Australian film): The romantic interest is molested by her dad.
Savage Grace: The film focuses largely on the real-life incestuous relationship between heiress Barbara Daly Baekeland and her son.
The Savage Is Loose: The film is a 1974 vanity production from George C. Scott about a couple shipwrecked on an island with their infant son. As the boy grows from toddler to puberty, he spies on his parents making love. As a young adult, he is suddenly competing with his dad for his own mother for the sake of lust. After getting rid of dad, the boy returns to conquer mom, only he can't bring himself to it. Dad returns and the film ends with a Power of Love message. The film was critically reviled for its overtone of parental incest to the point where Scott sent out bulk messages to movie theaters entreating patrons to see the film as a message of the bonding of a child with his parents.
The Secret (2007): Being in her daughter's body means things get very awkward between Hannah and Ben. He chides her for acting overly affectionate while they're at a restaurant, and later she's also quite suggestive toward him while wearing a pretty revealing nightie. They never actually cross the line, but it was obviously difficult for them still wanting intimacy but unable to because of the bizarre happenstance.
17 Again (2009): Mike's daughter briefly falls for him, not knowing that he is her dad. Thankfully, it doesn't go any further than that.
Sleepwalkers (by Stephen King): The mother and son cat-people villains regularly indulge in this, since sex is the only way for the son to transfer life energy to his mother so she can stay alive. They're apparently the last of their kind, though.
Soapdish (a movie that parodies soap operas): Narrowly averted. Celeste, a soap opera superstar, starts acting... suspiciously when her former lover and co-star Jeffrey takes her niece Lori on a date. Later, when he's about to kiss Lori, Celeste completely freaks out, tearfully revealing that Lori is actually their daughter whom she gave up when she was born under pressure from the television studio. Naturally, everyone starts remarking on how this is very much like the plot of a soap opera.
Society: Bill is horrified to discover that his parents have been engaging in orgies with his sister. After he discovers that they're actually humanoid monsters who can distort their bodies, his sister even mockingly invites him to join in.
Something About Amelia (a 1980s Made-for-TV Movie): The plot is about the 13-year-old title character revealing that her father (played by Ted Danson in a Golden Globe winning role) has been doing this to her for two years.
Spanking the Monkey (an (in)famous indie film): A drunken assignation between the lead character and his mother leads to him leaving home at the end.
Splice: Dren with both of her/his parents, although technically Clive is only a step-parent, at best.
The Strange Thing About the Johnsons: The titular "strange thing" is that the son is raping his father. Albeit at the end the son claims that the father instigated it.
Sweeney Todd: The Demon Barber of Fleet Street: While she's not his biological daughter, Judge Turpin wanting to marry his adopted daughter Johanna (with all that entails) certainly qualifies. Turpin also had a serious lust toward Johanna's mother, Sweeney's wife, which set the entire plot in motion with the awful things he did in pursuit of it.
Tank Girl: The titular character makes a joke about how "It's like the first time you get laid! You gotta say, '"Daddy, are you sure this is right?'"
Three Seats for the 26th: In this French film starring Yves Montand as himself and buxom sex bomb Mathilda May as his illegitimate daughter Marion (a character created for the movie, not based on any real person), they meet and, not knowing that they are parent and child, feel attracted to each other and eventually have sex. The Reveal comes when Marion's mom tells her that Montand is her biological father. Marion isn't shocked or anything, she just makes an "oopsie!" face. Later, the two go tell Montand the truth. Montand, unlike Marion, is shocked, and looks at her daughter with a horrified face... but Marion just smiles and shrugs, which makes Montand relax and realize that Parental Incest is not such a big deal after all. They all become a happy family.
Trilogy of Terror: The Millicent and Therese segment is about two sisters who hate each other. Millicent claims that Therese seduced their father when she was sixteen. Since Millicent and Therese are actually the same person, it's likely that this is an... uncharitable interpretation of what actually happened.
Unspeakable (2000 indie film): James Fhelleps loses his teenage daughter in a car wreck, then goes on a killing spree when he thinks his daughter is talking to him through a dead hooker, pleading with him to save her. After this ends in his death, it turns out to be a dream, caused by guilt over his incestuous molestation of his daughter.
Volver (by Pedro Almodovar): The film has Attempted Rape by Paco towards Paula. Later, we learn that poor Paula was conceived in a manner similar to Katherine from Chinatown.
Some supplementary material states Freddy once beat and raped his mother.
Womb: A woman impregnates herself with the embryonic clone of her dead lover, brings him up to adulthood, and proceeds to have a sexual relationship with him again. Technically, it is not incest as the "parent" and "child" do not share any DNA.
Wrong Turn: The inbred family of the series are prime examples of this. We even get to see one of them give birth in the second movie, which spawns a very deformed member of the family.
Year One: Zed rather casually admits to laying with his mother, although he does say he felt rather awkward about it in the morning.
