Actually I had downloaded an GUI for graphviz (dont remember the site), which said that they had won an Apple Design Award. But that tool really only displays an *.dot file I created. That's it. It's just called "Graphviz"... I guess that there are better tools around for using the Graphviz technology.
I tried this one: link text
Although they say that they won an Apple Design Award, I really can't see any special GUI there. Very poor interface.