From the Internet Archive: Prelinger Archives (http://www.archive.org/movies/prelinger.php):
Prelinger Archives was founded in 1983 by Rick Prelinger in New York City. Over the next twenty years, it grew into a collection of over 48,000 "ephemeral" (advertising, educational, industrial, and amateur) films. In 2002, the film collection was acquired by the Library of Congress, Motion Picture, Broadcasting and Recorded Sound Division. Prelinger Archives remains in existence, holding approximately 4,000 titles on videotape and a smaller collection of film materials acquired subsequent to the Library of Congress transaction. Its goal remains to collect, preserve, and facilitate access to films of historic significance that haven't been collected elsewhere. Included are films produced by and for many hundreds of important US corporations, nonprofit organizations, trade associations, community and interest groups, and educational institutions. Getty Images represents the collection for stock footage sale, and some 1,600 (soon to be 2,000) key titles are available here. The collection currently contains over 10% of the total production of ephemeral films between 1927 and 1987, and it may be the most complete and varied collection in existence of films from these poorly preserved genres.
At the PA, you can watch scores of public-domain films in amazingly good quality for their age. Some of them you may have heard about, like Duck and Cover, or seen on Mystery Science Theater 3000, like A Case of Spring Fever or Hired!. There are also vintage ads, such as the I Like Ike campaign spot.
So, you may be asking, What can I do with the PA? Well, the vast majority of films are from the 1940s-1960s; every one of them represents some facet of the culture contempory to the time it was produced. Want to see World War II propaganda justifying Japanese interment? Check out A Challenge to Democracy. Wondering how your parents came of age? Molly Grows Up or As Boys Grow will probably surprise you. And there's no shortage of Cold War marterial. For any student of 20th Century history, the PA should be required viewing.
Or maybe you just want to burn them to VCDs, invite your friends over, get drunk, and have a campy film festival.