PHP Bible by Tim Converse & Joyce Park is probably the most detailed and extensive publishing for PHP Development I've ever seen. Of course I own a copy myself, but this book might be alot more expensive than the average PHP development guides; well worth your money. I've learned how to create custom features for my site and integrate them with vbulletin using the tutorials from inside.
It starts out very simple, in-fact, I had to skip about 10 chapters because of the obvious simplicity. If you're looking to learn every little detail involved with PHP, you'll get it stuck by the end of the book, if you ever have time to excell that far. I'm about half way in, and I'm currently working on my own content management system for my site. A month ago, I didn't even know what a php include was!
I recommend this to anybody, begginer to advanced.