Based on code by Andrey Vityuk. I updated it from scala 2.8 to 2.10, put it in an sbt project, and threw in misc enhancements.
You need graphviz installed. brew install graphviz or equivalent, and then:
# or make up your own class names
visualize scala.Mutable scala.util.Random
That will generate .dot files in target/dot. If things are going well, it might also generate pdf visualizations, and if they're going really well, it might even display them for you to gawk at.