Gnome Music Player Client is a frontend for the Music Player Daemon. It’s focused on being fast and easy to use, while making optimal use of all the functions in mpd. This is the icon I created for it:

Update 03.07.2008: Added Play, Pause, Disconnected icons for 22×22 and 16×16 versions for the tray icons

Update 11.07.2008: Pause icons have now orange lines