Refcardz are free cheatsheets written by book authors and industry experts on a wide range of technical topics for developers including Java, Spring, Windows PowerShell, EJB 3, Ajax, Design Patterns, Silverlight 2 and many more. They are released weekly and so far there are over 20 of them available for developers to download for free. Each of them are 6-8 pages and they cover everything from how to get started with the tool, shortcuts, tutorials, diagrams, useful tips, source-code examples, and so much more. They recently released a PHP refcard written by Jason Gilmore.

Download the PHP Refcard here:
http://refcardz.dzone.com/refcardz/php