Here are some of my favorites--all of which are classics:
Touching the Void-the worst mountaineering expedition that anyone ever survived. Would you cut the rope if it meant killing your friend and saving yourself?
Dog Town and Z-Boys-The birth of modern skate culture in the 70's.
Spellbound-the intense, real-life experience of the National Spelling Bee as seen through the eyes of eight young spellers.
Bowling for Columbine-Michael Moore tackles America's obsession with firearms
Roger and Me-Michael Moore tackles layoffs from the GM plant in his hometown, Flint, MI.
Hoop Dreams-follows inner city kids aspiring to be in the NBA.
Super Size Me--Morgan Spurlock eats a lot of McDonalds.
Any film by Errol Morris:
Fog of War-Former Secretary of Defense McNamara's thoughts on war and why it's f'ed up.
Thin Blue Line--Racism and so-called justice in Texas.
Fast, Cheap and Out of Control--this one is wacky, but I like it. There's really no way to describe it and do it justice. It's about a lion tamer, a mole rat researcher, a robotics specialist and a gardener.