The American Film Institute has picked the top 100 quotes from American movies. Slublog has a couple of quotes that didn't make the list, but should have.
Personally, I would have liked to see a couple of lines from Clint Eastwood's Unforgiven:
Bill Munny: Hell of a thing, killing a man. Take away all he's got and all he's ever gonna have.
The Schofield Kid: Yeah, well, I guess he had it coming.
Bill Munny: We all got it coming, kid.
Or this one:
Little Bill Daggett: I don't deserve this... to die like this. I was building a house.
Bill Munny: Deserve's got nothing to do with it.
And of course this one from Fight Club:
[after vigorous sex with Tyler Durden]
Marla Singer: My God. I haven't been fucked like that since grade school.