BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
TubeLister - Generate a YouTube playlist from your opened tabs.
Gnoosic - Even if you don't know what you are looking for - gnod will find it.
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