Hotscripts.com :: PHP: Extensive collection of over 6,400 free and commercial PHP scripts and applications, all searchable and arranged by category. Also includes books on PHP, articles, and other PHP-related resources

osCommerce: A free online shop program featuring order history, shopping carts, full search capability, product reviews, secure transactions, bestseller lists, and related items

PHP Builder Support Forum: Very active forum with categories for PHP and database questions

PHP Manual: Complete and hyperlinked manual documents and explains all elements of PHP. Includes FAQ section and user comments