Free PHP Books and Sample Chapters
Programming : PHP at wikibooks 
This is an open content php textbook from wikibooks. It covers the basic of the PHP language as well as some advanced concepts such as OOP and templating.
PHP 5 Power Programming
To download the book for free as a pdf file click on downloads under the More Information heading and a div will appear with the download link.
Practical PHP Programming
This is an unpublished book on PHP. This book assumes no PHP programming skill at all - you will be taught from scratch in that respect. It appears to be quite comprehensive and can be navigated online in tutorial fashion, so it serves as an online php book or php tutorial.
Learning PHP 5 Sample Chapter
Chapter 8: Remembering Users with Cookies and Sessions
PHP Cookbook Sample Chapter
Chapter 8: Web Basics
Programming PHP Sample Chapter
Chapter 5: Arrays
A Programmer's Introduction to PHP 4.0
Free PHP book online that can be downloaded in pdf format.
PHP Session Management With Cookies
Book excerpt at O'Reilly.