I came up with a number of documentaries for class. If I saw more movies, I'd have a better selection but as a start:
Home Movie - directed by Chris Smith. Features five unusual homeowners, one who lives in a missile silo, one in a treehouse, one in a houseboat, two with 11 cats in a giant "Kitty Condo," and one in a fully automated house that he can control by remote.
Fast, Cheap, and Out of Control - directed by Errol Morris. [Insert ex-girlfriend joke.] A look at life itself (which the title refers to), featuring an animal trainer, a topiary sculptor, a robot designer, and a scientist who studies naked mole rats.
Pumping Iron - George Butler and Robert Fiore. A look at weightlifting, featuring, among others, a pot-smoking future governor.
Spellbound - Jeff Blitz. Children competing in the National Spelling Bee. Nine-year olds spell words that I wouldn't even attempt with a spell-checker.
Gimme Shelter - David and Albert Maysles and Charlotte Zwerin. The Alamont Rock Festival of 1969, complete with on-screen murder.
Triumph of the Will - Leni Riefenstahl. Should wake up even the most apathetic student.
Paradise Lost: The Child Murders at Robin Hood Hills - Joe Berlinger and Bruce Sinofsky. If Triumph of the Will doesn't cut it.
The Lumiere Brothers. 85 short documentaries of Louis and August Lumiere from 1895 to 1897.