Muzzy - it’s a tiny and gorgeous iTunes companion that lives on your menu bar. For Mac OSX, its free!
EarTrumpet - Volume Control for Windows
SpotiMy - Play/Pause and Next/Previous functions for Spotify directly on your Menu Bar!
Volume2 - Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control.
Skip Tunes - Control iTunes, Spotify, or Rdio from your Mac's menubar
Sound Control - App-specific volume control