Momixa - Pick two songs and get the perfect mix
Songstack - Swipe to discover new music for Spotify
The Best Song - The fun way to discover good music
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
FIEND.fm - "Hot or Not" for music discovery: 2 hrs of tracks in 2 mins
22tracks - DJ curated Spotify playlists on iOS