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.
Musicroamer - A visual Pandora for discovering new music
DiskyT - Youtube playlists done right
TasteDive - TasteDive recommends similar music (musicians, bands), movies, TV shows, books, authors and games, based on what you like.
OrganizeTube - Create video playlists from Youtube, Vimeo and other sources