Graphical GUI for Graphviz on Mac?

I assume you mean pixelglow.com which is a nice implementation of graphviz, I believe it includes dotty. If dot writing isn't actually a requirement you might check out the following:

Omnigraffle is by far the best app on the Mac for making graphs but it cannot export back to dot, and is not free (but does have a 20 object free limitation).

Gliffy is also nice (webapp).