In this new post on the PHP Women blog, auroraeosrose talks about one one the newest features in the latest PHP 5 series release - the Filter extension.
In response to a lot of griping from the PHP community about a lack of unified cleaning of user supplied data, 5.2 is introducing a new extension included by default, called filter.
She points to some of the resources associated with it - the manual entry and a short tutorial on the topic to get you started. She also mentions something newbies to the extension might not know - that it does two jobs, sanitizes and validates.