UbuWeb - contemporary (and some modern) avant-garde film and video by a wide variety of directors and artists from Laurie Anderson, Brian Eno, Marina Abramoviç and Claes Oldenburg to Picasso and the Lumiere Brothers. Free.
Open Culture - 500+ free films, mostly from 1900-1990. Browse titles.
Includes such classic films as
GreenCine Movie Primers: Primers on Film Genres
Iincluded on this site, for instance, is an overview of Battleship Potemkin and Sergei Eisenstein, found under "Russia: 1896 - 1953" in the list of film genres.
Early Cinema - find biographical information on the pioneers of cinema, such as Jean Méliès (under "pioneers" on left, then select name of director)
Palace Classic Films - find hundreds of images, a comprehensive bibliography, and some articles on movies and filmmaking.