The Zend Web Site

http://www.zend.com

The Zend engine is the engine that powers PHP. The Zend Web site is the site of the company that puts out the Zend engine, as well as many other tools. For example, at this site you can also download the Zend Optimizer, which gives your PHP scripts a 40-100% increase in speed on average.

In addition to great software (even if it isn't all freeware), this site also contains an active online message board ( powered by Phorum), and many articles and tutorials about everything involving PHP (I write for them). One sample article by Andi Gutmans (co-creator of the Zend engine), which takes you under the hood of the Zend engine and describes all the exciting new features. Another sample article is an article by Till Gerken on how to create and manipulate images with PHP.