Gnoosic - Even if you don't know what you are looking for - gnod will find it.
TubeLister - Generate a YouTube playlist from your opened tabs.
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
OrganizeTube - Create video playlists from Youtube, Vimeo and other sources
Musicroamer - A visual Pandora for discovering new music
Vidlis - Create music playlists from YouTube videos.