Cooper watches a video of Laura and Donna at a picnic, and spots James' motorcycle reflected in Laura's eye.
Cooper bluntly putting Bobby in his place by saying four words to him in regards to his refusal to work with Coop: "You didn't love her." Bobby is immediately silenced and Coop just quietly orders to have Bobby to be taken out of the room. Bad ass.
"Episode 1"
Garland Briggs informs his son Bobby that he understand his troublesome behavior is part of a necessary rebellious state that is required for his complete development as a human being, and although he respects and loves his son he is required to keep his behavior within certain familial and societal boundaries (slaps Bobby to knock the cigarette out of his mouth) and even though Bobby and the town are going through some difficult times, he will ensure that Bobby finds out what's important and who he truly is. (It's understandable why Garland was in so few scenes, he could've easily taken over the show since he arguably makes even Cooper look bland by comparison).
"Episode 6"
Though her machinations ultimately end up with her getting captured and almost killed, Audrey's slick manipulations as she gets her way into One-Eyed Jack's are admittedly pretty awesome.
"Episode 7"
Andy shoots Jacques in the arm before he can shoot Truman.
Season 2
"Episode 10"
Albert's speech about being an adamant pacifist, particularly at the end when he says "I love you, Sheriff Truman." Available here. It's one of the best moments in the show.
After finally remembering about what Laura told him in his dream about Leland being her killer, Cooper manages to trick BOB by making him think that he's really taking in Ben Horne for the crime and that he'll need Leland as his lawyer. Then, once they reach the station, Cooper pulls Harry aside and whispers in his ear the truth just before they reach the holding cell. They then manage to shove BOB in the cell in place of Ben at the last second.
As the police leave with Ben Horne in cuffs and Leland trailing, Garland Briggs, Bobby, and Hank regroup and look at each other (and then at the departing authority figures) in slight bewilderment. Cooper, the last of lawmen to leave, turns around to face them just as he reaches the door, and flashes them a smile and thumbs up. The next shot is of the elderly waiter, who smiles and gives Cooper a salute in return.
Pete demonstrating his chess prowess by winning three simultaneous games.
"Episode 23"
Norma's complete dismissal of Hank when he's less than flattering about her relationship with Ed: "I'd rather be his whore than your wife."
"Episode 28"
The entire Miss Twin Peaks sequence in the second last episode. firstly, the revelation that Lucy is an extremely talented dancer. Then the fact that Annie wins, although this takes a tragic turn seconds later. THEN Windom Earle's entrance disguised as The Log Lady. And also the Log Lady herself fighting off the choreographer's advances.
Andy figuring out the map to the Black Lodge.
"Episode 29"
On the villainous side, BOB stopping Windom Earle from taking Cooper's soul, saying that Earle broke the rules and that he's going to take Earle's soul instead. Sadly diluted by BOB going on to trap Cooper in the Black Lodge himself immediately afterwards, but it managed to finally put Earle in his place after the latter had spent the latter half of the season playing a literal and figurative chess game with innocent people's lives in order to mess with Cooper.
The Return
"Part 2"
Cooper's dopplegänger's introduction. He beats up on some redneck giving him shit and when the redneck tries to fight him again, the dopplegänger knocks him out, all the while talking in a calm manner.
"Part 4"
After Cooper drinks some coffee, he's able to emote and say something that isn't just parroting back what he's heard.
From a character stand point, Denise's progression from a simple undercover agent for the DEA and rising all the way to being the FBI's Chief of Staff.
"Part 6"
Janey-E's epic rant at Tommy and Jimmy regarding the loan and the extremely onerous interest they're imposing:
Janey-E: Okay, so you get this straight. My husband has a job, he has a wife, he has a child, he does not make enough money to pay back $52,000 for anything. We are not wealthy people. We drive cheap, terrible cars. We are the 99 percenters. And we are shit on enough. And we are certainly not gonna be shit on by the likes of you. So here's what we're gonna do. Without my knowledge, my husband came to you for a loan of $20,000. You were nice enough to give it to him. But he should never have been gambling like that. I'm gonna pay you back. Now, at my bank, where we make less than one percent interest on what little money we have, people would be turning cartwheels just to get 25 percent interest on any loan, and that is what I'm generously gonna give to you right now, $25,000. That is my first, last, and only offer to you. What kind of world are we living in where people can behave like this? Treat other people this way without any compassion or feeling for their suffering? We are living in a dark, dark age, and you are part of the problem. Now, I suggest you take a good, long look at yourselves because I never want to see either of you again.
"Part 7"
After a few episodes of Empty Shell antics, watching Cooper stop Ike "The Spike" in his tracks when he pulled out a gun, and quickly disarming him with a few Cooper-chops was some damn fine awesomeness.
"SQUEEZE HIS HAND OFF"
"Part 13"
Mr. C arm-wrestling with Renzo (played by Derek Mears) and winning manages to be both this and Nightmare Fuel. His whole strategy consists of allowing him to nearly win before returning to starting positions and eventually wearing him out and twisting his arm towards the table and finally pinning him down. Then he literally dents his face in with a single punch. Talk about ruthless.
"Part 14"
Sheriff Truman taking Chad into the conference room, only for Hawk to pull a gun on him and Truman to cuff him. After seeing him be a douche for the last few episodes, this is incredibly satisfying.
While drinking alone at a bar, Sarah Palmer is harassed by a drunk redneck who gets increasingly rapey despite her attempts to rebuff him. She responds by removing her face, revealing an empty void with a grinning mouth beneath, before immediately tearing his throat out. Talk about The Reveal!
"Part 15"
Richard attempts to threaten Mr. C with a gun, only for the latter to easily disarm him.
. It's one of the best moments in the show.