Concertmaster - Classical music front-end for Spotify
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
Music-Map - The Music-Map is the Tourist Map of Music, part of Gnod, the Global Network of Discovery.
Songstack - Swipe to discover new music for Spotify
Poly-graph Hip Hop - See what hip hop's billboard top 10 sounded like
Music Walker - Explore and play (via YouTube) songs similar to a seed song.