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
Volume Icon - Volume Icon aims to be a lightweight volume control that sits in your systray.
Power mixer - Power Mixer is a complete Windows volume control replacement.
Volti - Volti is an GTK+ application for controlling audio volume from system tray/notification area.