I think the best movies I've ever watched high are Monty Python movies. They are definately better high. Movies that I have to think too much tend to make me sleepy. I did try to watch the Doors movie, as someone mentioned, but recall that I felt like the movie took forever, and eventually fell asleep.

Overall, I like to pick out something funny, because it is usually funnier. Someone mentioned a philosophical slant on movies, and that' not a bad idea, as long as it is interesting. Try Butterfly Effect for something like that - every time I watch that, I find something new I missed previously.