Primer: the best movie I've seen all year...
I recommend not reading anything about the movie ahead of time, because half the fun is figuring it out for yourself... and you have to be patient at the beginning, as it starts out pretty slow... but it's worth it... just pay attention!
After you've seen it see it again until you understand it as best you can, then watch the director's commentary. Then read the Imdb and PrimerMovie message boards. And finally, there's this.