Spotalike - Spotify playlist with similar songs, according to Last.fm
EarTrumpet - Volume Control for Windows
MusaicFM - An iTunes like screen saver based on Spotify and Last.fm
Sound Control - App-specific volume control
Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...
Power mixer - Power Mixer is a complete Windows volume control replacement.