I can recommend one NOT to watch while tripping - Antichrist by Lars Von Trier. Willem Defoe and Charlotte Gainsbourg go to a cabin in the woods and everything just goes insane. When a self-disembowling fox says 'Chaos Reigns' to the camera you know it's all a bit weird. Excellent film which draws on the salem witch trails and has a bit of an occult thing going on but it gave my girlfriend a panic attack so best avoided whilst under the influence!

I saw that again recently... soooooo good!

Pihuechenyi, i just watched the trailer for Antichrist and it looks really messed up. I wanna watch it... but definitely not while tripping.

Lots of great stuff already mentioned - notably Baraka and Koyaanisqatsi. Let us not forget also:
Powaqqatsi: Life in transformation (1988 )
Naqoyqatsi: Life as war (2002)

I tend to mute the "Qatsi trilogy" aforementioned and put different music on however - even in groups, we have experienced some amazing synchronicities while watching.

My personal favs:
Mulholland Drive - Exceptional piece of mind bending, immaculate film making.
2001: A Space Odyessy
Primer - Best time travel film. Ever.
Milo and Otis - such a nostalgic film for me.
Gummo - Haunting film by Larry Clark
The Machinist
Pink Floyd, The Wall
Children of Men - Really is one of my favourite films of all time
Earthlings - Must see documentary on animal exploitation and the meat industry.

There are loads more!

My friends and I speculate that DMT is what he's vaporizing inside the light bulb.

I don't think the adrenochrome is supposed to represent ayahuasca. They say it's the blood/fluid from the adrenal gland from a human body in the movie, although it is a real substance, of which the psychoactivity is highly debated.

http://www.erowid.org/chemicals/adrenochrome/adrenochrome.shtml

I'd say Waking Life. Also, Blueberry is an awesome movie with some legit Aya trip visuals.