Two I haven't seen mentioned:
http://imdb.com/title/tt0166896/ The Straight Story, though not strictly a documentary
"The Straight Story" chronicles a trip made by 73-year-old Alvin Straight from Laurens, Iowa, to Mt. Zion, Wis., in 1994 while riding a lawn mower. The man undertook his strange journey to mend his relationship with his ill, estranged, 75-year-old brother Lyle. Written by Christian Sandberg
Alvin Straight is a very old man with a quiet life in a small country town. When his brother gets seriously sick, he decides to put away their differences and visit him after many, many years. So, alone, he begins a long journey through hundreds of miles, just to see again his brother, even if it's the last thing he will ever do... Based on a real story. Written by Chris Makrozahopoulos {makzax@hotmail.com}
AND
http://imdb.com/find?s=all&q=southern+comfort Southern Comfort
At its essence, Kate Davis's film, Southern Comfort, is about a transgendered man who is dying from cancer in his female reproductive organs. Southern Comfort is more than this, however. It also deals with the intricacies of the social community that the main character, Robert Eads, has surrounded himself with since transitioning from female to male, details the romantic attachment that Robert has formed with his girlfriend Lola Cola near the end of his life, and examines the dynamics between Robert and his genetic family. More than this, Southern Comfort engages in a discourse on human sexuality that serves to enlighten the audience viewing the film on the realities of transgendered life in the backcountry of the Deep South.