EarTrumpet - Volume Control for Windows
Volwheel - VolWheel is a little application which lets you control the sound volume easily through a tray icon...
Sound Control - App-specific volume control
Volti - Volti is an GTK+ application for controlling audio volume from system tray/notification area.
Power mixer - Power Mixer is a complete Windows volume control replacement.
KMix - KMix is an application to allow you to change the volume of your sound card.