This list is not intended to be comprehensive, but it will serve as a good starting point for those seeking hard to find media or doing film-related research.
MIT Libraries Film Studies Subject Guide your local resource for scholarly film research and writing.
Museum of the Moving Image, Moving Image Source a comprehensive research guide that contains resources on criticism, industry, as well as online film and video sources.
Internet Movie Database the de facto online database of commercially released films.
Ubuweb Film and Video a very large repository of avant garde film and video organized by artist. This is a great source for hard to find items if you know the author/director. All clips stream directly from the site.
Society for Cinema and Media Studies Interested in the world of film studies beyond MIT? The is the largest professional organization of film and media scholars in the US.