Well, if i were to take the logical route, i would suggest "Asta la Vista, Baby", as i garentee you that even if you were to ask someone who had no idea who the actor or movie was were that phrase came from, EVERYBODY would be able to tell you it's a movie. It's known by 4 year old's and 67 year olds. Everybody knows it, hence, by ingraning itself into society's memory, it is THE most memorable line.
But........
Seeing as this thread is also about personal opinion, my most memorable line would have to be....
ENGLISH ************, DO YOU SPEAK IT?