A while back Alan Forbes started a Kickstarter project to write a PHP book, "The Joy of PHP". This book was targeted at those that wanted to learn PHP and "have some fun along the way". The book has been finished and, in a special promotion, is being offered free of charge through Amazon and for the next five days.
The book "The Joy of PHP" by Alan Forbes now available as a Kindle book on Amazon.com. Starting today (or tomorrow, depending on Amazon) and lasting only 5 days the book will be absolutely free. The only "catch" is that the author is asking for reviews. In other words, once you've taken a look a the book please go back to the book listing on Amazon and give it a star rating from 1 to 5 to help the author build momentum for the book.
You can find out more about the book on its website and, if you don't want the Kindle version, pick up a copy of the PDF version for just $12 USD.
UPDATE: the free offer for this book has been extended and is available for no cost for a limited time!