For another film....Wizards by Ralph Bakshi anyone? Please tell me I'm not the only person here to have seen it.
This is one of my favorites for dissociatives. I wouldn't go so far as to call it a bad trip inducer for 5HT psychedelics, but it has this sickly color palette and if you look close you'll see there's scary faces drawn into all the landscapes. The story is sort of demented and dark, too -- with this smurfs vs. Nazi trolls vibe going on that has to be experienced to be believed.
Wizards trailor
Dissociatives afford me an aesthetic distance that makes movies like these, horror, and things like cigarettes in oil stained dank parking garages in winter look beautiful. I feel the same way about Felidae, which was already mentioned. It's got scenes with cats torturing each other with electricity and other mean gritty stuff.
Heavy Traffic is another Bakshi great, though not as trippy, but again there's this sick schizoid PCP in the 70s atmosphere permeating the thing. American Pop has parts where the protagonist trips on acid and stuff, and is worth checking out if you like the first two mentioned a lot.
Heavy Traffic
EDIT: The Triplets of Bellville is trippy in a sort of unconventional way. In theaters the Salvidor Dali/Walt Disney short "Destino" was shown before it -- that one is serious surrealism (blasted 50 mg DPT IM and stumbled into the theater for it, heh). It's not on the Triplets DVD unfortunately, but I'd think you could probably find online somewhere.
Destino:
Another forgotten trippy animated gem is Allegro Non Troppo. It was meant to be the Italian answer to Fantasia. Like Fantasia, it consists of a number of animated vignettes rendered to great classical pieces. It's darker and more adult themed than Fantasia, which is pretty cool, too.
Allegro Non Troppo
Here's
the "Bolero" segment. It's this cool "humans as killer apes/evolution" short.
I would also call the Rebuild of Evangelion films extremely trippy and worth a watch (and I say that as a person who finds 99 percent of anime intolerable -- not least the type involving giant robots -- but this is an exception). The trippiness extends more from the themes, the vivid color palette,the design of these creatures called "Angels," and the ridiculously high production values. Watching them in HD is pretty stunning. Know that there's only two of four movies out, and the forth is slated for 2013.
It's not an animated version of an LSD vision or anything, but if you're at all intrigued watch
this segment to see what I mean.