Can’t remember when this happened to me but after some upgrade in the past my gnome-volume-control-applet just stop appearing in my notification area. From what I understand this is due to the full integration of Pulse Audio in the last linux builds, but either way it was a pain in the arse as this little tool is the easiest way to be adjusting your volume. After some searching I found a quick fix and that was to simple go into System > Preferences and add the following to the Startup Applications list:
gnome-volume-control-applet
That should do it, upon bootup you should have it back and if you don’t want to wait till you reboot just press alt-f2 and run it there. Viola! Problem solved
