"Frankly, my dear, I don't give a damn", Clark Gable in "Gone with the Wind", has been judged the greatest line of all time in a film.
Two lines by Marlon Brando, "I am going to make him a offer he can't refuse", from "The Godfather" and "I coulda been a contender" from "On the Waterfront" were second and third on the list.
I thought that "Sin from my lips? O trespass sweetly urged! Give me my sin again." in Romeo and Juliet would have been considered as one of the best movie lines. But "ya see, folk prefer when they use this fucking language."
Sorry! :-s