Christopher Martinez has a recent post to his site that covers some of the static analysis tools available for PHP including the PHP Mess Detector, PHP CodeSniffer and the PHP Analyzer.
I believe in writing code that is easy to understand, easy to test, and easy to refactor. Yes, I realize that the statement above is pretty general and open to interpretation. Not everyone needs external tools to ensure quality in their code...but, I work on things from time to time that have absolutely no tests. [...] For whatever reason, this happens a lot more frequently in the PHP world. I'm guilty of not writing tests and checking how I write code, sometimes, too. Things are bright, though, for the PHP community - for quite some time now, we've had fantastic tools that assist us in writing better code.
He covers each of the tools, talks some about what they're good for and gives examples of their use, including output. He also talks some about the Pfff set of tools created by Facebook. He also talks some about how these tools fit into his daily work as a part of his pre-commit hooks in git.