Playlist Machinery - Tools that help you create & organize your Spotify playlists
Spotalike - Spotify playlist with similar songs, according to Last.fm
Party Blends - A way to blend your friends favourite tracks into one Spotify playlist.
MusaicFM - An iTunes like screen saver based on Spotify and Last.fm
Ranked Records - Create Spotify playlists with all an artist's songs
Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...