Let us now praise the public domain, for it has given us the more than 100 movies that I have added to the sidebar under the heading "The Canon Fires 24/7" (scroll down) including dozens of silent films (Méliès, Griffith, Sjöström, Epstein, Eisenstein) and many sound ones too (Hitchcock, Capra, Lang, Hawks), and lots from the avant-garde (Man Ray, Deren, Brakhage).
I started poking around a few days ago to see how much cinema is available streaming and free online now. I was prompted by a discussion at CinemaTech, noting a subscriber-only WSJ article, about silent films online being given new life with fresh soundtracks (CT links to versions of A Trip to the Moon and Nosferatu). I wasn't that surprised by how much I found, but it is remarkable that this simply did not exist a couple of years ago. It is now possible to acquaint yourself with a substantial and representative chunk of film history, at least of film history in the West, without leaving your desk. You could certainly program an entire online film history course based around these offerings, though you might not want to go much past WWII. Of course I would prefer to see these films as good prints projected well, but as an educational and scholarly resource this online alternative is quite clearly a remarkable thing. I wish this had been available to me when I was a youngster keen to know more about the movies.
There is lots more out there including many more Griffith Biograph films, Brakhages, Sherlock Holmes movies, exploitation films, studio-era animation, and more contemporary experimental stuff. Search Google Video and you will find it. There are tons of clips from films online, which I avoided. I wish I had found more non-Western titles. Perhaps if I could read more languages I would have better success with that.