Mpd-applet shows an icon representing the state of the mpd server and allows to do play/stop/pause/prev/next. Finally, a user selectable client can be started from the popup menu to do the more complex stuff.
Have a look at this thread in the forums for screenshots and installation instructions...
The sources can be downloaded from here.
A binary Debian package can be downloaded from here.
For questions and bugs: daniel-mpdapplet_at_lindenaar_dot_org