From a post on Drawn! found out that the National Film Board of Canada is showcasing entire short films for free on its site. The quality of the video is ok, although the size is pretty small by default, you have a large format version available. I've have some problems with them, but I don't know if that's because of the actual demand or just my Quicktime plugin on Firefox, I'd suggest the flash version for most users. I haven't seen them all so far, but two I've seen that I already know are the ones by Cordell Barker and classic animation master Norman McLaren. Oh, and my all time short animation favorite by Christopher Hinton, Blackfly.