ERASERHEAD (1977)
Some Surreal Herzog:
EVEN DWARFS STARTED SMALL (1970)
THE ENIGMA OF KASPAR HAUSER aka EVERY MAN FOR HIMSELF AND GOD AGAINST ALL (1974)
HEART OF GLASS (1976)
STROSZEK (1977)
FITZCARRALDO (1982)
I don't know if I'd consider
Fitzcarraldo too surreal, but it's certainly got its odd moments and it's really a lovely and majestic film. And
Stroszek isn't too unusual until the end and it becomes something else entirely and I love it! I think
Aguirre, the Wrath of God and
Fata Morgana also qualify.
2001: A Space Odyssey has been mentioned and I'm still feeling the effects from watching it last night. It's my second viewing and it was just as powerful as my first. You know what would be awesome? Since this was originally released with some 70mm prints, Warner Bros. ought to have some 70mm IMAX prints made and release this next year for its 40th anniversary. Watching this in an IMAX presentation would be amazing.
Other mind-benders:
The Trial (1962) -- This is an awesome and frightening Orson Welles film based on the Kafka novel.
Picnic at Hanging RockSave the Green PlanetThe Illustrated Man -- This is a very flawed film, and not exactly a great adaptation, but it's pretty weird and open ended.
A. I. -- I think this movie is underrated.