Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...
EarTrumpet - Volume Control for Windows
Muzzy - it’s a tiny and gorgeous iTunes companion that lives on your menu bar. For Mac OSX, its free!
Sound Control - App-specific volume control
Owlead - Grow your Twitter with valuable followers, effortless
Power mixer - Power Mixer is a complete Windows volume control replacement.