Fear and Loathing is just OK imho.... here are some real true trip flix:
Imaginarium of Dr. Parnassus (Terry Gilliam's latest, Heath Ledger's last)... trippy as all fuck.
Alice In Wonderland!!!
Brazil
Time Bandits
Adventures of Baron von Munchhausen
Monty Python and the Holy Grail (only if you want to be rolling on the floor laughing uncontrollably... its old but still works... timeless brilliance)
Cheech and Chong's Nice Dreams (if you never saw it yet, rent and see whole thing all the way through... its really one made for tripping... do NOT go watching the VERY trippy ending - with Timothy Leary - crappy looking low res you tube screen grabs... it will SPOIL the ending of the movie... just rent it and watch tripping or smoking joint after joint so you are BLASTED by the ending)
2001 (probably a bit slow and drawn out if you are tripping, but still highly awesome and epic)
Matrix 1,2 & 3
The Fountain
Breakfast of Champions (lots of big stars, trippy comedy also very touching, inspired by but different from Vonnegut novel... ignore all the "just dont get it" reviews by stupid cranky squares around the net and by critics... if you watch this high or tripping, which I strongly recommend, YOU WILL GET IT, and be laughing your ass off and possibly tearing up by the end.... GREAT "Exotica" trippy 1950's "Lounge" music soundtrack is another plus)
Renegade (originally Blueberry, dir by Jan Kounen... who lived with Amazon shamen and tripped for a year... cover looks like a crap Western but its really an initiation story and there are 3 long elaborately visualized trip sequences that come closer to anything ever done to realistically visualizing the high dose hallucinogen experience.... VERY otherworldly and highly long and complex... DO NOT SPOIL THE FILM FOR YOURSELF AND JUST VIEW THE LOUSY TRIP SEQUENCE RIPS YOU CAN FIND ON YOU TUBE!!!! On their own the sequences are kinda "cool but huh?" but make real sense and advance the plot viewed IN the film... the entrances to the scenes are also mysterious and build atmosphere... and also the trips RESOLVE PLOT POINTS. Do your drugs, wait for them to hit, put it on big home theater speakers, dim the lights and hit play.... seeing the trips for the first time ever within the whole film WHILE YOU ARE TRIPPING, having NO idea what to expect is VERY intense and entheogenic! WELCOME TO THE REAL WORLD)
Stay (REALLY wildly trippy!)
Sixth Sense
Dark City (new Directors cut with 11 unseen minutes)
Star Trek: The Motion Picture (revamped with redone CGI effects that now look awesome and are very very trippy, and which has one of the most ecstatically hallucinogenic endings you could never imagine)