Some of my favorites:
Inside North Korea
http://www.imdb.com/title/tt0987374/A crew of journalists sneaks into NK under the premise of being doctors. It's a insanely good look at conditions Koreans face everyday in the north under a brutal dictatorship.
A Film Unfinished
http://www.imdb.com/title/tt1568923/?ref_=nv_sr_1A series of pictures and films are discovered that show unedited footage of life inside Jewish ghettos during WW2. What's so amazing is how much information it gives historians who are forced to reevaluate conditions in the ghettos. They were much worse than we originally thought, since the Nazis created propaganda films which historians had based their facts on.
This Film Is Not Yet Rated
http://www.imdb.com/title/tt0493459/?ref_=nv_sr_1This documentary analyzes the history of the MPAA and how they're used to bully small, independent films. Meanwhile, they give different ratings to high-paying films with similar content.
Worth looking into if you have time:
Restrepo
http://www.imdb.com/title/tt1559549/A documentary that follows a group of U.S. troops operating in the Korangal Valley during our war in Afghanistan.
The Union: The Business Behind Getting High
http://www.imdb.com/title/tt1039647/?ref_=nv_sr_2A history of marijuana and its illegality in the U.S.
Waiting for Superman
http://www.imdb.com/title/tt1566648/?ref_=nv_sr_1Filmmakers follow several students as they navigate the public education system looking for better opportunities.