PHPBuilder

http://www.phpbuilder.com

The documentation on PHP is an awesome reference, but some of the more abstract concepts of PHP can't be covered by a simple function reference; they need to be explained by experts who have been there and done that. PHPBuilder offers an impressive set of tutorials ranging in level from beginner to advanced. I find gems there all the time, such as "Building your website with cached dynamic modules" (JP) and "HTML_Graphs" by Tim Purdue. This site also includes links to a code repository and an active message board system.