22tracks - DJ curated Spotify playlists on iOS
Magic Playlist - Get the playlist of your dreams based on a song
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
Spotalike - Spotify playlist with similar songs, according to Last.fm
Spotify - Map shows when two people play same song at same time
Playlist Machinery - Tools that help you create & organize your Spotify playlists