The PHP Security Consortium has officially launched today. The consortium is made up of a leading group of PHP experts that are dedicated to promoting secure coding practices within the PHP community. If you are interested in learning about writing secure code for your web applications, keep an eye on this web site.
Updated 2021 : note that the above post is out-of-date, given this post was originally published in 2005, but is left here for archival purposes. I have unlinked the PHP Security Consortium website (http://phpsec.org/) as that is now dead.