Java and C++ programmer mostly confuses the Reference and Alias mechanisms of PHP. This small tip will help you to understand these. There is also a simple but very interesting code included.
This column by Rod Kreisler explains what classes are, why they are useful and how to use them in PHP. He then goes through with the creation of sample classes providing code so you can see the methodology behind it all.
Some concrete examples of using object oriented principles in PHP along with plenty of sample code that helps guide you through the learning process.
This April, 2000 article by Luis Argerich introduces Object Oriented Programming in PHP an explains the concepts behind data type abstraction, inheritance and polymorphism as it related to PHP.
This article presents programs that aid in code documentation, as well as tips on how to better document your code so that it is more useful to both yourself and others.
This article takes a look at class design with PHP4 along with some of the available classes and how to use them in your code.
This tutorial, designed for intermediate to advanced PHP developers, teaches you how to write and use classes to make your PHP code more flexible and easier to manage. | 
