Over a year ago I posted an XSL file for prettying up Graphviz diagrams
I got lots of feedback, and recently I've been fixing various bugs, and I finally got around to adding support for more of the Graphviz node shapes etc.
Here's an example of various node types and colors with the new version. Note that while rounder corners are "sort of" working, I haven't found a good way of making the gradient fill work nicely with it. The current version has been tested with Graphviz 2.20.2.