Good Day Mom Kat
Right now, I would have to say two are my favorites.
"By the way, if you talk to that sheriff of yours again, or you don't show up at four o'clock, I will burn your life and every person in it like a cane field in a high wind." (Secret Window with Johnny Depp and John Turturro).
"I guess you think I'm kicking ya, Bob. That ain't so. What I'm doing is talking, you hear? I'm talking to those villains down in Kansas; and I'm talking to those villains down in Missouri; and all those villains down in Cheyenne; and I'm telling them there ain't no whore's gold! And even if there was, they wouldn't want to come looking for it, anyhow." (Unforgiven - Gene Hackman, Clint Eastwood, Morgan Freeman, Richard Harris).
The latter is a favorite of mine because it encapsulates the dynamic of the film. Gene Hackman, who said the line, did so in a very violent context, the behavior seems thuggish, however Hackman is the sheriff or marshall of the town. Clint Eastwood is the "bad guy" in this film but he is, of course, more "sympathetic." The relationship between good and evil is handled in an interesting way.
The line from Secret Window is one of my favorites, well, because its so cool. It has to do with the words, the context, and the way John Turturro ("Shooter") says the line.