Event Horizon /thread
Seriously though, like Chakra said, Quarantine is pretty good.
The Japanese versions of The Ring, get the American one if you can't find it.
American one isn't bad but the Japanese one is just that much freakier.
Oh, yes. That movie is ****ing awesome. Quarantine IS a pretty awesome movie too, but it's not the happiest of movies, but if you want that girl to get real cuddly I would go with that. A lot of dark scenes with things popping out at you (not penises). The Thing is also up there with Even Horizon. Two classic, tried and true, can't fail horror movies.
Since horror movies are in discussion, I would like to say that I preferred the American version of Ring of the Japanese one. The Japanese one I didn't find scary at all, and I usually enjoy Japanese/foreign movies. Speaking of foreign horror, I hear Audition and High Tension are very good. I have not watched them myself yet, but I hear they're very scary/****ed up.
The first 2 Alien movies also never fail. They're not the scariest of movies, but they're up there on the "oh, ****!" level with black slimy aliens popping out at you and what not. Not to mention they are just awesome movies. I've also watched Alien with a girl and she subsequently played with my penis that night if that gives you any more confidence.