The creators of PHP and keepers of the language.
Site includes comprehensive documentation, source downloads, etc.
Zend Technologies Lot's of information on PHP, including their optimizer. Good place for beginners to start. PHP Resources at DevShed A good set of articles introducing various PHP concepts phpWizard PHP Tutorials, scriptlets, quick reference, plus they are the keepers of phpMyAdmin, a very cool web app written in PHP to make managing mySQL databases much easier. LinuxGuruz Has some great info on PHP, including PHP and mySQL tutorials. Plus, their innovative web-based admin interface gives you complete control over creating mySQL databases and assigning users.