BeatSense - Discover great music hand-picked by real people, in a single click. FREE and in real-time!
Magic Playlist - Get the playlist of your dreams based on a song
FIEND.fm - "Hot or Not" for music discovery: 2 hrs of tracks in 2 mins
Spotalike - Spotify playlist with similar songs, according to Last.fm
MusicJet - Sharing links to promote all of your music, tickets and merchandise with a unique page and get insights into your fans
Playlist Machinery - Tools that help you create & organize your Spotify playlists