A swathe of PHP programming links that I find useful.
This includes links such as the PHP home site and PHP developer sites. The developer sites that I find useful include sites hosting various class libraries such as PEAR and phpclasses.org.
Of course another place to search for PHP classes is just using Google, since there are so many of them scattered around the web these days.
PHP programming language home site.
A commercial distributor of PHP products including the Zend engine (for optimising) and Zend studio, an IDE for PHP.
PHP Extension and Application Repository. This is supposed to form the PEAR core class repository, much like CPAN does for Perl. Some of the stuff here is very useful (eg: the DBI layer), some highly complex (error handling), and some of variable quality.
A useful site containing PHP articles and HOWTOs, class libraries, news, etc.
A large grab-bag of PHP classes of variable quality.
A huge grab bag of PHP, MySQL and JavaScript code snippets, some organised into classes and some not.
An example of a content management framework, built around PHP (although not in PHP). Where I believe that Midgard falls down is that although the core library is formed from OO classes, the "snippets" style programming approach forced on the Midgard user (developer) actively discourages OO programming.
In my experience this turns (very poor) ASP code into very poor PHP code.
Available in dead-tree and digital/download editions.
Another script collection -- at last count it boasted over 8500 PHP scripts. Free registration.