PHP Builder
Contains numerous articles and tutorials on using PHP to perform various tasks and functions. Also includes a support forum and links to other resources.

PHP Tutorial from Tizag.com
Includes a nice tutorial on the basics of PHP.

PHP Tutorial from Troubleshooting Professional Magazine
Includes a nice tutorial on PHP to which covers numerous topics that are helpful when coding in PHP.

PHP.net
Downloads, documentation, reference, news, and more on PHP.