Here's a little snippet I got from SitePoint that I now use all the time. Add the code below to the start of each script.

Basically, what this does is checks to see if magic_quotes_gpc() is enabled on the server, and if it is, then it gets rid of all the slashes that magic_quotes_gpc() adds to input from $_GET, $_POST and $_COOKIES globals.

It's a good snippet to use, because it negates the bad programming practices that having magic_quotes_gpc() lets you get away with, and means that you don't really on PHP to validate your input; you get to do it all yourself ;-)

A little function that does some basic checking for data input by a user. Should get rid of code injection ;-)

This simple function will check if a url is valid (going by parse_url()) and if it's 'online' - by seeing if it returns a 302, 301, or 200 status code.

This small snippet will not allow _POST requests from a 'foreign' domain. It relies on the HTTP_REFERER variable.

This function will reverse the affects of register_globals

This is a simple PHP script that will show whether a certain port/socket of a certain computer is currently open/active.

This multiple-use PHP script will randomly generate content based on a randomly generated number.

This code illustrates using ruby REXML package. It converts J2EE web application deployment descriptor web.xml into Freemind mindmap document.

Make External Links Open in New Window

This detects screen resolution using javascript and makes it available to php by way of cookies.