Magic Playlist - Get the playlist of your dreams based on a song
MusicTwin Finder - Find your MusicTwin by your Spotify playlists in 5 seconds.
Spotalike - Spotify playlist with similar songs, according to Last.fm
SoundCloud Charts - The most played tracks on SoundCloud this week
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Spotify - Map shows when two people play same song at same time