Waking Life
Harold and Kumar
Easy Rider
Requiem for a Dream
Ray
Training Day
Dazed and Confused

Oh, and it isn't a movie, but the TV show LOST is unbelievable when you're high. You have to start watching from the first episode though, because the show plays like 1 long movie. Nothing is resolved at the end of an episode.

That's all I got off the top of my head