IndieVolume - IndieVolume makes Windows programs use separate volume controls independent of other Windows...
EarTrumpet - Volume Control for Windows
SoundBunny - SoundBunny allows you to control the volume level for all open applications on your Mac.
Volume2 - Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control.
Volwheel - VolWheel is a little application which lets you control the sound volume easily through a tray icon...
Volti - Volti is an GTK+ application for controlling audio volume from system tray/notification area.