PHPSecInfo is a great tool to use to keep an eye on your production environment. It was written by Ed Finkler of CERIAS, the Center for Education and Research in Information Assurance and Security at Purdue University. It is officially a project of the PHP Security Consortium.
The tool allows you to easily run a security audit against your system and find the issues in a familiar phpinfo() style of result. Remember, it's a starting place - not an ending one. Security is more than just running a script to check once and a while.