The most iconic:
"Here's looking at you kid"
Hands down the most recognized quote in movie history, pretty much everyone can put that black and white scene in their mind when they hear that.
Pop culture phenom:
"I'll be back"
Still quoted with a pathetic Austrian accent to this day.
My personal favorite however is much simpler, and I love it because of the delivery and set up of the scene. In Pulp Fiction, after Butch has screwed over Marcelles Wallace. Wallace has every set of eyes he knows out and and about looking for Butch with bad intentions. Then, in broad day light at an intersection, carrying a cake in a bakery box no less, Wallace casually walks right in front of Butch's car, turns to him and says "mother ****er..."
To this day I laugh my ass off everytime that scene comes up!