Jason Lotito has posted a small (but growing) [url=http://forums.devnetwork.net/viewtopic.php?t=29269]list of resources[/url] related to security and PHP. There are links to the [phpsec] mailing list and plenty of reads that will keep you busy for hours.
http://blog.bitflux.ch/wiki/XSS_Prevention
There are also pleanty of great links being added to the Jason’s list, so be sure to check it once in a while.
– Dan