My all-time favorite:
"I know what you're thinking: 'Did he fire six shots, or only five?' Well, to tell you the truth, in all this excitement, I've kinda lost track myself. But, being this is a .44 Magnum, the most powerful handgun in the world, and would blow your head clean off, you've got to ask yourself one question: 'Do I feel lucky?' Well, do ya punk?"
More of a scene than a line, but a good one.