The scene from Fargo where Peter Stormare (the dumb, insane, no-conscience-at-all serial killer) sits in that cabin watching a soap opera on TV while eating cerial, and the female character in the soap says "I`m carrying your child" (or something like that), and his jaw just drops. That`s the only emotional expression he has in the whole movie, and it`s over a scene in a soap (in another scene I think he dismembers someone while they`re still alive, and he doesn`t raise an eyebrow). That was so funny.
The "breakdown-part" in Requiem for a Dream, with the classical music playing in the background.
The montage in Rocky 2, where he`s training. I was 13 years old and jogging every night for two weeks after that one, while shadow-boxing, ha ha.
The spirder-scene in the new version of The Exorcist, where the girl comes running down the stairs on all four, on her back, like a spider. Poltergeist, where the little girl is watching the TV. The intercourse-scene in Enemy at the Gates. They are doing it in a trench-like scenario, with lots of other soldiers lying around, everywhere, sleeping. But they just have to do it. It`s incredibly both erotic and romantic (which is a hard thing to accomplish, in itself) although very little skin is revealed.
All of Donnie Darko (the best movie ever made).