php.net has everything. when i run into a problem, i always google it and php.net will be at the top of the list.
If you want a book on the subject, I found the WROX book "Beginning php 5 to be better for me than the highly reccommended Oreilly book. It just seems to be written a little easier to read. Plus you can download all the sample scripts from their site. You may be able to find a better deal on the book somewhere besides their site. I bought mine new at a local bookstore for less than 50% of the cover price.
PHP.net, ultimate resource to learn php. Other than php.net, I recommend http://www.phpfreaks.com, http://www.codewalkers.com/