For some reason volume control widget is not showing on my Ubuntu panel. I reinstalled alsa and something else, because my sound broke. Now I can't get my audio control panel to display on Unity main panel.
Any one knows what is the problem?
For 14.04 and 16.04 From the launcher - System Settings -> Sound make sure the box shown at bottom left is checked.
Alternatively you can launch from the command line with
gsettings set com.canonical.indicator.sound visible true
Worked for me.