This is just a quick announcement that I have released a Kohana 3 module for CSRF prevention on our github account. This module could easily be ported over to your favorite PHP framework if you modify the CSRF_Form class to handle creation of your FORM tag.
sample code on the github page
handles special case AJAX implementations
user agent validation
user-defined timeouts (expiration)
private key salted two-way encryption using mcrypt
the PHP mcrypt module (php-mcrypt or php5-mcrypt depending on your distro)
jQuery >= 1.3.2
Questions, comments, and concerns are all welcome.