THX 1138 was another one. It's kind of a credit to George Lucas that his film school short ended up being produced by Coppola when it came time to make the feature length version.
Sam Raimi and Bruce Campbell did it with The Evil Dead, as well. Yeah, shit low budget horror film, but so fantastically done that the main character is completely integrated in pop culture to this day. The thing with it is these are highly talented (if a bit oddball) people, and the signs of talent are obvious even if the material is schlock. That and none of these shorts involve a dance at a nazi death camp where all the condemned girls fall in love with the ss guards.