Jack O'Connor, managing to crash the terrorists' computer systems entirely with his virus, taking out all the cameras and the V1 ending off the air. Unfortunately this happened, how shall we say? Somewhat late...
He also gets another posthumous crowning moment of awesome when his virus is reintroduced to the terrorists' systems, poleaxing them again, this happening in version 3 - more than two years after Jack's death.
Adam Dodd's fights with Cody Jenson and Jacob Starr could count, particularly since they were among Adam's biggest rivals in the game (in the second and first half respectively).
Bryan Calvert dropkicking Felix Travertil off a roof, causing him to smash through the skylight of the adjoining antebuilding. Badass? Why yes, yes he is. The incident is famous enough that his handler (the real life Bryan) has a picture of himself dropkicking a tree.
Darnell Butler laying out 'Boxer' Carvalho, who was more than seven foot tall, and built like a brick wall, in what amounted to one punch. This coming after Darnell just killed three people who attacked him. Beware the Nice Ones indeed...
For reference, Darnell is a foot shorter and almost one hundred pounds lighter than Boxer.
Sean O'Cann's very Deadpan Snarker -esque sarcastic comments when cornered inside a room between two of the island's resident murderers: Gabriel Theobaldt and Dominica Sharpiro, are his Crowning Moment of Awesome.
Sean: You see why I call the guy a lunatic? * he frowns, having been called a ''young virgin metrosexual'* Hey, enough about my sex life: just concede that I have a far higher chance at getting laid than either of you and be done with it. Hell, it would be a minor miracle if Gabriel could meet any woman and spend more than a minute without disembowling her. * He looks at Dominica* And rest assured, I would come up with a suitably witty remark concerning you, however, I have no fucking clue who you are.
Character Derailment notwithstanding, the SADD vs. Blood Boy (one of the bigger villains of the first half of version 3) fight was one of the most action packed and all-around awesome moments of the third game so far. Read it here (the action starts at around page 4).
Speaking of SADD, Bobby Jacks' encounter with the group is definitely one of his best moments. Keeping his cool in the face of a giant Mexican Standoff (Bobby vs. Everyone else) Bobby manages to calm down the situation, and when things finally go to hell, both walk out of the fight completely unscathed and kill three people, granting him the distinction of being the only guy to pick a fight with SADD (the largest group in Survival of the Fittest v1-3) and come out on top. The Thread.
Ethan: "If Iím going to die, I want to be taken out by the final boss, not by some kid from the chess club. I donít want any of your circuitous bullshit about a classmate killing me. In the end, itís you. If you hadnít done this to us, they wouldnít be killing. Even if they kill, itís still you in the end. I donít want you to be able to hide behind a scared kid. I want my blood on YOUR hands. I deserve to be killed by you."
Eve Walker-Luther also earned one at the hands of Sarah Atwell. This is when she's being tortured.
No matter how you feel about the mechanics behind it, let's face it; Liz Polanski deactivating her collar using melted aluminum is freaking awesome. To get an idea, it incited a Mass "Oh, Crap!" from the terrorists. Even with what comes after (Danya randomly killing characters and later sending a death squad to the island for both this and her destroying cameras afterwards) it still has that punch.
In The Program v2, Maxim Senders comes across Chris Brooks on the first day. Having robbed someone before, Maxim tries to do a "repeat performance". Only, though, Chris has this to say about it:
"Fuck you." Chris said holding up his bloody middle finger to Maxim's face. He wasn't going to let someone try and intimidate him. Not when he was in a life and death game.
In Virtua v1, "Big Mike" Gibraltar is facing Brian Larke. Mike has a cake, Brian has a shotgun. What does Mike do? Run at Brian and smash the cake in his face. He doesn't get very far before getting killed, but it's still one of the most audacious ways to attack someone.
When I get to Heaven, I am so telling Anton that I threw a cake at Brian.