Titan Panel has a build in Gold Display module that does exactly what you are looking for.
As far as I remember that only displays the players CURRENT gold. I think the op wants an addon that can tell you how much you've actually made excluding what the player had before.
The built-in currency module for Titan Panel will display your character's gold, your total server gold, the gold earned during your current session, aswell as your avg gold/hr income (or deficit)