Titanic - From the point in the film where the ship sinks up until the end, like I think someone said before. Even before you see the film, though, you kind of know the ending. You know the ship will eventually sink. I think one of the actors said that "you'd do anything you could to stop that ship from sinking" when you watch the movie. And they're right.
A Walk to Remember - When Jamie tells Landon she has cancer, when he says he will always be there, and when [SP]Landon asks Jamie to marry him.[/SP]
Atomenent - The last ten minutes or so, when you find out about what happened to Robbie and Cecelia. (sp?)
Love Story - When Jenny tells Oliver "I want time. And that's something you can't give me." Or something like that. And of course, the end.
The Notebook - The end, and also when Allie is reading Noah's last letter to her in the car before she goes to see Lon.