Brick
Saw Brick last night and it was excellent.
Kind of a Chinatown-esque film noir thingy, only all the characters are in high school. It's not like the movie goes on about it though ("oh, look, they're in school, how delightfully witty"), it's just a kind of unusual setting for an excellent detective story. Twisty story, too. I really like having to concentrate to follow the plot; such a nice change from the average movie where the ending is a foregone conclusion.
Beautifully shot, witty, never a dull moment. Highly recommended.