An impressive sum of links and good articles on PHP, worth reading!
This list of recommended reading material on PHP is compiled from a variety of online sources by Web application developers in IBM's Global Production Services organization. These resources have been selected with the intention of introducing IT specialists and architects to PHP, providing specific information about development and maintenance, and helping to integrate the technology with IBM products.
PHP is an interpreted programming language run in an environment provided by an open source core engine and extensions whose development is driven by many companies and individuals. As such, this list describes resources that apply to writing PHP programs and to customizing the interpreter's environment. It links to material published by IBM and content provided by others. From IBM developerWorks