EarTrumpet - Volume Control for Windows
Background Music - Control the audio on your Mac apps from the menu bar
3RVX - 3RVX is a skinnable volume display and controller.
Power mixer - Power Mixer is a complete Windows volume control replacement.
Audio Sliders - Volume Control replacement that is five times smaller than its Windows counterpart.
Volti - Volti is an GTK+ application for controlling audio volume from system tray/notification area.