Land and Freedom, in its entirety. It's a film about a young English Communist who goes to fight the fascists amidst the Spanish Revolution as a member of the POUM militia. He sees both the reality of a people's revolution and the consequences of Stalinism. It's directed by Ken Loach, who also directed Bread and Roses and The Wind that Shakes the Barley. Subtitles will help a lot if you don't speak Spanish.
The Scots voice of the Spanish revolution [Embedded DivX video 1hr15m; also downloadable] Ethel MacDonald was a young working class Scots woman who hitch-hiked to Barcelona to do her part in the war. There she became the English-language voice of the anarchist movement as a radio station announcer. Newspapers at home dubbed her the "Scottish Scarlet Pimpernel" for her role in helping comrades escape the crackdown that followed the May Days. Her remarkable story is told in this recent drama-documentary.
B. Traven, A Mystery Solved [Flash video, 1hr] Excellent documentary on the astounding life and mysterious identity of the author of Treasure of the Sierra Madre [Flash video, 50mins] and The Death Ship.