Sonar - code quality management platform
Sonar enables you to collect, analyze and report metrics on source code.
Sonar not only offers consolidated reporting on and across projects throughout time, but it becomes the central place to manage code quality.
Sonar currently covers Java and PL/SQL languages. However, Sonar is highly extensible and can therefore embark plugins to cover new languages.
Very simple to install: http://docs.codehaus.org/display/SONAR/Install+Sonar
and use:
http://docs.codehaus.org/display/SONAR/Analyzing+Java+Projects
There is also Hudson plugin that makes it even simplier to run sonar on the build server: http://wiki.hudson-ci.org/display/HUDSON/Sonar+plugin