Magic Playlist - Get the playlist of your dreams based on a song
Spotalike - Spotify playlist with similar songs, according to Last.fm
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Spotify - Map shows when two people play same song at same time
Doppler for iPhone - A better offline music experience for iPhone
SubmitHub - SubmitHub makes it easy to contact music bloggers, Spotify playlisters, record labels and more. We give you all sorts of statistics and ways to filter who to send your music to.