Professional Search Engine Optimization with PHP: A Developer's Guide to SEO

I've read a number of other resources on the subject of SEO, and this one is definitely the best I've encountered. No one aspect of SEO is particularly technically complicated, its more just a matter of being aware of all the areas in which you can help (or more likely, not hurt) yourself. This book does a very thorough job of covering all of these areas, and is clear and concise when it comes to describing specific tactics and the underlying mechanisms that make them effective. Also, as mentioned by another reviewer, this book can be a valuable resource to a non-programmer because of how clearly it explains all of the tactics it covers and how involved the case studies in it are.