From their site:
UbuWeb: The YouTube of the Avant-Garde: UbuWeb has converted all of its rare and out-of-print film & video holdings to on-demand streaming formats Ã la YouTube, which means that you can view everything right in your browser without platform-specific software or insanely huge downloads. We offer over 300 films & videos from artists such as Marcel Duchamp, Vito Acconci, Pipilotti Rist, Jean Genet, The Cinema of Transgression, Richard Foreman, Terayama Shuji, Paul McCarthy Jack Smith, Carolee Schneeman, John Lennon and hundreds more — of course all free of charge. Presented in conjunction with our partners at Greylodge.
Here is the link to their video index.