1.Hoop Dreams. Also, probably the most important movie about sport in America ever made. And it's only a little about sport. When I saw it for the first time in a theater, I sat in my seat weeping for 20 minutes after. If you have ever dreamed of athletic glory or thought that sport was a force for good in our society and if you care whether it is a force for good, you can't watch this film and remain unmoved.
2. If Ken Burns Baseball makes the list, then surely Civil War must be near the top. In documentary film history there are, figuratively, those films made before it and those after.
3.Finally, I might have missed it, but The Thin Blue Line is very very good. So good, it overturned a murder conviction. It's also at least a little about the limits of perception and memory and, if you're philosophically minded, about epistemology.