Black Canary: When Dinah and Ollie are together, they have a very active sex life, and in times where they're not together she's often shown to have an active dating life. However, though their relationship has been rocky from both sides, it's notable she's never been anything but faithful and honest even when he's not been.
DC Comics Bombshells: Downplayed with Mera. In addition to using her superpowers in combat, Mera entertains sailors and soldiers by singing, dancing and putting on shows. Supergirl condescends to her using her appearance in such a manner, but Mera retorts that her body and her powers are her own to use as she sees fit. Her beauty and performances helps raise morale and assists her compatriots in weathering the grueling trials of war, and she is happy to do so.
The Star Sapphires of the Green Lantern comics. They believe in love and the freedom to love in all its myriad forms, though this becomes hypocritical when it's shown that one of the Sapphires' weapons is a worldwide crystal prison and at least one of their Lanterns is a brainwashed former criminal. And originally the titular crystal would turn its bearers into rampaging Yandere, who would preserve their love for eternity (if it was reciprocated) by encasing the entire planet they were on in crystal. Now that they channel their power through rings the Sapphires have calmed down considerably.
Furthermore, the crystal prisons were also used to preserve one's love if they were in critical condition.
Their extreme nature is justified by how the Emotional Spectrum works. The farther one is away from the center (in this case, green, hence why Green Lanterns are associated with Willpower), the more influenced they are by the emotion. The Star Sapphires wield the Violet Light of Love with their counterparts being the Red Lanterns, wielding the Red Light of Anger. Being on the ends of the spectrum, they are not just influenced by their light, it overwhelms them completely.
What Starfire was supposed to come off as in Red Hood and the Outlaws, although she had sex with only one person off-panel in one issue. While the general idea behind this was consistent with her previous characterization since the 80s, in which she was portrayed as an Innocent Fanservice Girl and All-Loving Hero, the handling of it was generally considered to be botched badly and eventually resulted in her removal from the team. Her own series, Starfire (2015), goes back to having it as an extension of her generally loving and caring personality.
Alias: Luke Cage, according to Carol Danvers at the start of the second arc. She says he likes sleeping with superwomen (including protagonist Jessica Jones, onscreen, and Carol themselves; Carol also lists Jessica Drew, Tigra, and She-Hulk), to which Jessica responds that she thought he was a Nice Guy. Carol insists that he is a good man and his sex life has nothing to do with it. For his part, Luke says when Jessica challenges him on it that if he was a lawyer, he'd probably mostly sleep with lawyers, and points out that she came on to him.
Alpha Flight: Aurora likes men and she likes sex, and don't you forget it. Don't, however, confuse that with her manipulating men with her sex appeal. Northstar did, and that led to Aurora altering her powers to give herself space from him.
Within The Avengers, both Iron Man and The Wasp qualify. Tony is quite The Casanova, but despite his history of being a war profiteer, of which he is genuinely repentant about and has suffered considerably to atone for it, he's generally one of the most moral, if pragmatic, Avengers (at least until Civil War happened, but after this blew out he's come to repent and regret this, too). Janet meanwhile was always flirting with her teammates, and after her divorce from Hank Pym, she romanced many partners, including Iron Man himself, under his civilian alias (though when she found out Tony's identity, she broke things off because he was one of her ex-husband's best friends). Though both have their share of flaws, they're generally some of the nicest people to be friends with and treat all the Avengers like family, even the minor ones they have little history with, and just so happen to also be fond of sex.
Jennifer Walters aka She-Hulk is one of the nicest, most idealistic characters in the Marvel Universe, enjoys sleeping with others as long as it is consensual on both sides, and has one of the longest lists of partners of anyone in the MU. Note that this is only in her She-Hulk form. While she retains all of her memories and same basic personality in both forms, some of her views and personality traits are different.
Natalie in Gore Angels enjoys graveyard sex and admits to watching porno videos, but is fairly pleasant and is disgusted and furious to find out that Ryan raped Emiko, delivering a Groin Attack to him with her fist.
Most of the characters in the original +100 run, where casual sex is less of a taboo.
Moonstone Books' version of the Domino Lady tends to fall under this trope. The character is quite unapologetic about her many on-panel and off-panel liaisons, but she draws the line at sleeping with men who are involved with someone else.
The title character of Druuna is an incredibly erotic character who either initiates passionate sex on her own accord or is cajoled into it, but underneath her sex goddess exterior is very much a Nice Girl. The author specifically stated that he wrote her cavalier attitude to lovemaking to "challenge conventional notions of female sexuality".
Pretty much all of the elves in ElfQuest. Moonshade and Strongbow are a rare exception in that they're monogamous, but that has more to do with their relationship being too intense and introverted for other elves to enjoy.
In one possibly non-canon instance, even Moonshade proves willing to give an admirer a good time: "If all you wanted was joining (sex), I would not say no." Unfortunately, sex is not all he wants, and she eventually has to force him to realize that what he does want — that she change her nature to a gentle maiden instead of her fierce Wolfrider self — simply won't work.
For his part, Strongbow has no problem whatsoever with Moonshade offering to have sex with someone else, and is only annoyed by the admirer's clingy and circuitous behavior. It's a subversion of expectations to most readers when he grabs his lifemate's admirer by the lapels, gets in his face...and demands that he stop beating around the bush and ask for what he wants already, dammit.
In Forgotten Realms, Kyriani maintains dozens of casual relationships with adventurers and nobles in Waterdeep. Most of them are quite happy with the arrangement.
Tansy in God Is Dead. Though she is polite, kind, a strong believer in "love conquers all", and empathetic to those around her, she is also willing to use sex as a means of getting what she wants or simply to appease aggressors. Notably she gets insulted by Albert for believing “the path to peace is paved with blowjobs”.
Lori Lovecraft has a very active sex life, with an unending string of boyfriends, and is willing to fall into bed at the drop of a hat (or other item of clothing). However, she open about her free love philosophy with her partners, and her boyfriends are generally okay with her not being exclusive. Also she has never taken advantage of the Casting Couch to advance her acting career: preferring to win roles on her merits (such as they are) and saving sex for those she cares about.
Valeria: Valeria's lifestyle by the beginning of the story. Then she gets the very bad idea of trying monogamy. This is inherently a threat to her own life, being the kind of creature that she is, and opens her up to an attack that puts her lover in harm's way. Jennifer appreciates the monogamy, but that's without knowing the risks that comes with it. She imply that she would never have accepted that Valeria made this sacrifice for her, had she known what it meant.
The goddess Freya, in Valhalla. She is a completely shameless flirt and quite sexual, but she is ultimately more interested in love than sex. She finds the idea of a loveless marriage utterly abhorrent and refuses to so much as wink at married men.
Lucifer mentions the trope name in a conversation with Inanna in issue eight of The Wicked + The Divine, though what they've just done is only debatably "ethical".
Ah, to be ethical sluts. Only half of it perfected. You're a nice person...doesn't mean you're a good one.
Almost any non-villainous character in a work by Phil Foglio, but of particular note are Orgasm Lass of XXXenophile and Madame Louisa Dem Five of Buck Godot: Zap Gun for Hire who seem somewhere between confused and insulted by the idea that someone would actually choose not to have sex when given a willing partner. Lou runs a very high-profile brothel, so in her case at least turning down sex isn't just a perceived slur on her desirability as a partner, it's an aspersion on her very business. And even then, Lou backs off when told that the man she's coming on to has pledged a monogamous relationship to his partner.
