I've been working with a client recently who uses Sonar, an open source code quality management platform hosted at Codehaus. I'm thoroughly impressed with this tool. If you want to see what the tool can do without investing the time in installing it, take a look at the various screencasts. They also have a live version of Sonar up so you can play with it without installation.
We've been working on getting unit tests built around a legacy code base and Sonar has been a big help in identifying classes that are the biggest code coverage offenders. We used the Clouds feature, a word cloud that weights the class names in the cloud based on code coverage and complexity. The less test coverage on the class and/or the more complex the class, the larger the weight of that class name word in the word cloud. It really helped us focus on where to direct our testing efforts.
I have yet to get this tool up and running in one of my own projects, but things are finally starting to simmer down now with consulting and training activities that I hope to focus on building out a CI environment using Hudson and hooking in Sonar to that environment. Stay tuned.