Well, Youtube used to have a lot, but I think they've clamped down on that in recent months; particularly since the Google buy.
To be honest, I think you're better off downloading via torrent or other method. If you're already waiting a long time for episodes to buffer, you might as well be spending that time downloading a copy that actually looks and sounds decent. Depending on what kind of connection you have, and how popular the show is, downloading can be extremely fast anyway.