Author and long-time AWS developer Jason Levitt has just released his new book, The Web Developer's Guide to Amazon E-Commerce Service. Weighing in at 1.5 lbs and covering 492 pages, the book is centered around the use of PHP to create applications using ECS 4. All of the important base technologies are covered, including versions 4 and 5 of PHP, XSLT, REST, and SOAP.
Jason covers the E-Commerce Service, AIMS (Amazon Inventory Management System) and the Merchants@ API.
The book will soon be listed on Amazon.com; in the meantime you can order it directly.
Update: You may find this list of code samples to be useful.