I have so many that I can't choose just one!
1) Overboard - The scene where Dean goes after "Annie" when she returns to the boat as Joanna. And when "Annie" forces the boat around, and the two reunite because they love each other. And then again, the scene where Dean tells Annie she has everything she want and what can he give her? And Annie looks at the boys and answers " a daughter". I love this movie so much.
2) Jerry Maguire - The "You complete me" scene. So romantic.
3) You've Got Mail - The scene where Joe's waiting for Kathleen and she realizes she's been talking to him this entire time.
There's probably more, but I can't think of anything else at the moment.