Maybe it should be a sub-category, but I'll stack it here:
Favorite Romantic line in a movie.
From one of the most unlikely of films to have a line worth remembering, much less a romantic line, The Hot Chick.
"You're the only boy who makes my heart beat faster and slower at the same time."
For some reason that grabbed me.
As does this one from "L.A. Story". Steve Martin:
Harris: So there I was jabbering at her about my new job as a serious newsman - about anything at all - but all I could think was wonderful, wonderful, wonderful, wonderful, wonderful, and most wonderful and yet again, wonderful.
Same film:
Sara: And if I were to go?
Harris: All I know is, on the day your plane was to leave, if I had the power, I would turn the winds around, I would roll in the fog, I would bring in storms, I would change the polarity of the earth so compasses couldn't work, so your plane couldn't take off.