Man, I'm in a similar situation.
Small company (3 of us here, including the boss) and I do graphics.
I've done exceedingly more every year (website, 3D design and animation, IT) on top of what I was originally employed to do... not to mention a lot of the work we used to outsource I now do in-house because I do it better and faster.
I'd get raises annually but they're pitiful, so when I said something I just got a "I think you're paid fairly" response. Then you hear a sob story of how the company is doing in a review, how we can't really afford payrises, but then the boss will turn around to buy a sports car and 2nd house a couple months later.
So, my friend in the company quit 2 months back and I followed suit this week. Enough of this BS!