Get the Whitepaper called Finding Vulnerabilities in PHP Scripts. This write up comes filled with a large amount of useful examples and even provides fix information.
You can download it from the following link: https://packetstormsecurity.com/files/download/82058/findingphp-vulns.txt
Source: https://packetstormsecurity.com/files/82058/Finding-Vulnerabilities-In-PHP-Scripts.html