Many good ones cited! I love this threads!
That said: If it is more than 1 line or 1 sentence, it is not a movie "line," it is a "scene."
Some lines I liked (some of which have been cited already, but hey, why not repeat good ones!):
Taxi Driver: "You talkin' to me? You talkin' to me? You talkin' to me? Then who the hell else are you talking... you talking to me?"
Jerry Maguire: "Show me the money!" AND "You had me at hello."
Clint Eastwood ... many:
1) "Do I feel lucky? Well, do ya, punk?"
2) "You see, in this world there’s two kinds of people, my friend: Those with loaded guns, and those who dig. You dig."
3) "Go ahead, make my day."
4) "It’s a hell of a thing, killin’ a man. You take away everything he’s got, and all he’s ever gonna have."
Cool Hand Luke: "What we've got here is a failure to communicate."
Shawshank Redemption: "Get busy living or get busy dying."
Godfather - 1st 2 movies: Too many to quote ... like at least 5-6.
Jaws: "You're gonna need a bigger boat."
The Shining: "He-e-e-e-re's Johnnie!"
The Terminator: "I'll be back."
When Harry Met Sally: "I'll have what she's having."
For anyone who loves movies, there are dozens and dozens of great movie lines - and each person has lines that hit home more than others!