Movies ? Ever hear of reading a book ? Ha, just kidding.
Anything with death and dismemberment would be a bad idea. Any movie that is like a series of "short stories" is ideal. Like Joe Dirt, Monty Python movies (Holy Grail), Chris Farley (Tommy Boy, etc.) The Jerk, etc. A movie with a good stand-up routine might be a good choice too, like Richard Pryor, Sam Kinison, or George Carlin.
For a purely musical trip, There are 2 great tripping movies. Led Zeppelin's "The song remains the same" combines excellent music, interesting video's and great concert footage. Jimmy Page playing the guitar with a violin bow is insane. Pink Floyd's "Live at Pompeii" may be hard to find, but it's worth it. Same deal, great music combined with great video.
The best movie though, is definitely "Heavy Metal" (the original) followed by the sequel "Heavy Metal 2000." Great music with freaky cool short stories, sci-fi style.
I haven't tripped in like 10 years now. The only thing that would get me to do acid or shrooms would be to see a soccer game with COLLEGE FOOTBALL TEAM MASCOTS.
This weekend, I'm going to eat a bunch of cannabutter brownies, and trip out to Heavy Metal and Live at Pompeii