I won't be posting YouTube clips on my antiquated beast of a home computer, but the four of my many faves that come to mind at the moment include:
The first taunting video clip posted by the Joker, when he tells Batman-wannabe Brian Douglas to look at him... and then when the poor bastard hesitates, snarls "Look! At! Me!" Authentically chilling moment that brought out the underlying ferocity which was at the core of what made Ledger's rendition of the character so riveting. The vicious howling laughter overlaid with his victim's screaming at the end was even more chilling.
The guy who played 'Brad Bramish' -- clueless pawn of Laura, the piece's femme fatale -- had really good comedic chops. The parking lot scene where Gordon-Leavitt's 'Brandon' confronts him and lures him into a fistfight is classic. "Yeah?" "Oh yeah." "Yeah?!" "Uh, there's a thesaurus in the library... 'yeah' is under 'Y.' Go ahead, I'll wait."
Bill the Butcher was an incredible film villain: a man of indisputable sleaze and aberrant, piratical morality... but with his own self-consistent and ferocious code and the ability to genuinely respect, even to love, his enemy. The scene after Amsterdam Vallon saves his life -- when Amsterdam wakes up with the formidable Butcher sitting in a rocking chair beside his bed and watching him sleep -- is equal parts touching, tragic and creepy. "Oh, you got a murderous rage in you and I like it. It's life, boiling up inside of you, it's good."It was the scene that both demonstrated most vividly why people would follow the Butcher, or be tempted to follow him... and just how broken, twisted and doomed his view of life was. Daniel Day Lewis' finest hour, with all due respect to Lincoln and/or the drinking of milkshakes.
[Almost as good, from the same movie: the scene where the Butcher charges his tame cop minion Happy Jack -- former friend of Amsterdam's father -- to go out and kill the now-rebellious youngster and asks if the charge "sits uneasy with him." Happy Jack squirms a bit and says not exactly, but: "My allegiance is to the law. I'm paid to uphold the law." At which point the Butcher gets an authentically pained expression, puts his head in his hands and finally says: "What in Heaven's name are you talking about? You may have misgivings, but don't go believing that, Jack, that way lies damnation." Whole scene is brill.]
A lot of my favourite moments revolve around villainous monologues. Schwarznegger's 'Conan' has one of the best, delivered by James Earl fucking Jones himself while wearing a wig of truly magnificent absurdity. Evil immortal snake-priest Thulsa Doom, having caught Conan trying to infiltrate his Mountain of Power and had him beaten to within an inch of his life, confronts him and says "I wish to speak to you now," then airs his grievance as regards Conan's thefts from him and murders of his servants and, more importantly(!), his beloved pet snake. Conan quite reasonably points out that Thulsa Doom did exterminate his people, to which Thulsa Doom replies philosophically: "Huh. Must've been when I was younger." And then goes on to argue that Conan ought to be grateful to him for providing the young hero with motivation, illustrating his point about the "power of flesh" by having one his followers commit suicide. Fucking awesome scene.
EDIT: Oh! And one more:
The scene where Eamonn Walker's villain, James, is sent to murder a former friend on the say-so of his smarmy British arms-dealer boss Franklin. When it becomes clear that poor 'Darrell' won't mend his ways, James has them turn on some music, sings and dances along to a bit of Wang Chung's "Dance Hall Daze"... then says: "Darrell? Don't take this personal," stabs him with a sword-cane and stomps him into oblivion. Seriously heavy.