The milkman conspiracy level of Psychonauts is a great example of this, not only because the level design is so crazy and it defies the laws of physics, but also because the game takes normal every day concepts and twists them into something new and crazy, like the G-men in that level.
For people who haven't played the game, let me elaborate:
So here are some examples of games that I consider to be trippy
Super Mario Galaxy. I guess most people dont really consider this one weird, but I just love the innovative level design. I cant remember was it in SMG 1 or 2, but I think there was a level where there was cube of water floating in air where the player could dive and swim in. I guess because of the platforming nature of the game, most people dont really question that kind of stuff. And that's exactly the kind of stuff what I am looking for: level design that defies logic and laws of physics. Many early 3D platform games had levels that were just floating in black space/nothigness, I think it's often a lot cooler than a game realistic setting, like Toy Story 2 for example. If you have a Buzz Lightyear figure exploring mundane settings like a suburban house, then the level design, physics etc can't be very creative, it all has to follow conventional logic and rules.
The hallucination levels in Max Payne 1/2
The mystery vortex level of Sam and Max hit the road
The DLC levels of Alan Wake
Psychonauts
Kula World
LSD: Dream Emulator
Jumping Flash!
Nights into dreams
Weird dreams
Dream Zone
I actually haven't really properly played the Earthworm Jim games yet, but given how crazy the cartoon is at times, I assume the games are pretty kooky?
Alice the madness return and American McGee's Alice perhaps? Haven't tried those out yet myself.
Here are two Simpsons episodes that had the sort of weirdness that I'm talking about
http://en.wikipedia.org/wiki/The_Comput ... nace_Shoes
http://en.wikipedia.org/wiki/El_Viaje_M ... f_Homer%29
I think I should mention that in my opinnion, there is a some kind of line between trippy/surreal and crazy/Japanese(:P) games like Seaman, Little Big Planet, Katamari Damacy, Power Stone 2 and Lollipop chainsaw


