For Java code, I am a big fan of Sonar Source [1]. It is open source, is able to leverage checkers such as FindBugs, and has integration with code coverage tools such as Cobertura. I have found the clean dashboard to be a great boon, and have never felt intimated by the reported warnings like I've been with Coverity et al.
Please note: I have not used all of these; one day I was bored and decided to see how many code checking tools I could find packaged for Debian and put them all in a script with the warnings cranked to the max and make that part of my default nightly build and test script. Of course, you can also crank up warnings on your compilers and interpreters as well (-Wall -Wextra, python -tt3 with warnings.simplefilter("always"), perl -tTW with use strict and use warnings, etc)
[1] http://www.sonarsource.org