Magic Playlist - Get the playlist of your dreams based on a song
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Spotify.me - Beautiful analytics on your Spotify listening habits 🎧
Join My Playlist - Listen to music live together with your friends in Spotify.
Spotify - Map shows when two people play same song at same time
Pandora Thumbprint Radio - A hyper-personalized station based on the songs you've liked