AFANA is an organization dedicated to acquiring, promoting and preserving academic film and other historically important films in the fields of art, history, social science, literature and science. With the help of the Internet Archive, they are preserving some truly hidden gems of non-feature film making in the U.S. Check out their website.
One of my favorite films is this lovely little animation of butterflies and dragonflies set to the music of the French Baroque composer Francois Couperin.