There are a lot of documentaries freely available on YouTube.
Sometimes the producers release them for free, but most often other people upload the films and the copyright owners don't bother with taking them down.
xDocumentaries is a central place where you can easily find these documentaries...
Environment, 2005, with Joaquin Phoenix, 1 hr 36 mins
A 2005 American documentary film about humanity's use of other animals as pets, food, clothing, entertainment, and for scientific research. The film is narrated by Joaquin Phoenix, features music by Moby, was directed by Shaun Monson, Executive Produced by Libra Max and was co-produced by Maggie...(show more)
A 2010 American documentary written and directed by Josh Fox. Nominated for an Academy Award for Best Documentary in 2011, the film focuses on communities in the United States affected by natural gas drilling and, specifically, a method of horizontal drilling into shale formations known as...(show more)