Robin Good: If you are looking for a good curated resource for video documentaries, and you are not looking just for mainstream stuff, Chockadoc provides over 32 different collections and over 2000 free video documentaries, immediately viewable online.
Categories include everything from "health" to "war". See all the categories isted here: http://i.imgur.com/I39C7.jpg
The service is free, it requires no registration and it is ad-supported.
Try it out now: http://www.chockadoc.com/
Via Robin Good