From 1941 to 1943, Fleischer Studios and Famous Studios produced a series of 17 short Superman films which are now in the public domain. Google Video and the Internet Archive both offer downloads of the shorts, which are well worth the bandwidth.
- Superman a.k.a. The Mad Scientist (archive)
- The Mechanical Monsters (archive)
- Billion Dollar Limited (archive)
- The Arctic Giant (archive)
- The Bulleteers (archive)
- The Magnetic Telescope (archive)
- Electric Earthquake (archive)
- Volcano
- Terror on the Midway
- The Japoteurs (archive)
- Showdown (archive)
- Eleventh Hour (archive)
- Destruction, Inc. (archive)
- The Mummy Strikes (archive)
- Jungle Drums (archive)
- The Underground World
- Secret Agent (archive)
More information about the series is available on Wikipedia and Amazon has what looke like a nice DVD set.