w3schools.com

They’ve got good references and tutorials for a variety of web languages and tools.

You know how to code. Orielly’s cook book for php will show you how to solve common problems with php and build a better understanding of the language.

Next, stand on the shoulders of giants. Download an open-source project that does something your interested in written in php and figure out how it works.

For example:

Wordpress uses a ’simple’ code structure that shows off good code standards. (without too much OOP)

Magento would be the opposite extreme; a great example of OOP, design patterns, php5 and the Zend Framework.