Oldish article by Czech surrealist film-maker Jan Svankmajer - famous for his weird and dark stop-animation films - about his participation in an LSD experiment in 1972.

Svankmajer on Youtube

Trailer to "Sileni"
Et cetera
Meat Love
Darkness/Light/Darkness * †
Flora
Historia Naturae
Virile Games - Pt. 1
Virile Games - Pt. 2
Dimensions of Dialogue Part 1 * (Slightly better quality clip of the opening Arcimboldoesque segment here)
Dimensions of Dialogue Part 2 *
Last Trick Pt. 1
Last Trick Pt. 2
Food - Breakfast
Food - Lunch
Food - Dinner
Punch And Judy
The Death of Stalinism in Bohemia (from memory, NSFW - includes collages of 18th century porn)

etc... (and tributes)

* personal favourites
† now I think of it, contains one possibly NSFW gag. As might any of the others.

Oh, goody! Youtube has Bill Plympton shorts too! (Assume NSFW unless confident otherwise.)