Over on php|architect's site, there's a mention from Marcus about a new book from No Starch Press called "Object-Oriented PHP: Concepts, Techniques, and Code" (by Peter Levin) along with a little review.
"Object-Oriented PHP" is ideal for the developer who wants to learn object-oriented programming in PHP. If you already know how to use objects under PHP 4 this will get you up to speed with PHP 5. If you don't know anything at all about object-oriented programming, what better way to start than with the straightforward approach of PHP?
He has good things to say about the book, noting that it's laid out well, provided ample descriptions about the code and concepts presented, and helps you get the most out of your PHP5 programming.
You can purchase the book directly from the No Starch Press website in either paperback ($39.95 USD), a PDF version ($19.95 USD), or a combination of both ($43.95 USD). There's even a sample chapter if you want to try before you buy.