In case you didn't already know about it, I just thought I'd drop a link to the Prelinger Archives
Since I suck at descriptions, have a nice Wikipedia article
Anyway, I was introduced to the Archives because Skip the AV Geek comes by the local science museum every month to show an old sci-fi/horror film, and some related short films from his collection. If I'm remembering correctly he's actually the curator of one of their collections, but I could be wrong about that. Anyway, I've enjoyed the Archives so much that I thought I'd spread them around. I wouldn't be surprised if some of you already know about it, but then again some of you might not.