2 movies immediately come to mind (sorry they're not documentairies);
"Koyanisqatsi" and "Baraka"
Both movies are only images & music, no words at all. I found this perfect to
watch on LSD or other, similair long-acting Psychedelics. I like to have little
pressure; Nothing demanding too much attention. You can watch it, but you won't
have to focus on what is said and what exactly is going on. It's easily digestable
for the mind: You won't have to think about it much. It's much more a sensory,
feeling experience than a cognitive experience. And such beautyfull scenes are shown.
Then there are documentairies I've enjoyed sober, but I am sure they'll be perfect
to watch on LSD:
-Chemistry: A volatile history
-Bruce Parry's "Tribal" series of docus (Specifically the one where he snorts Virola snuff with the Yanomami)
-Other Worlds (French Ayahuasca-Docu by Jan kounen, English subtitles)
-Shamans of the Amazon
-Hofmann's Potion (LSD docu)
-Inside LSD (Great LSD docu by National Geographic)
Those are the ones I could think of in a whim. Hope you will enjoy them.