Two weeks ago I read a book by Boris & Eugene Mordkovich named Pay-Per-Click Search Engine Marketing Handbook. The book has a tremendous amount of advice, strategies and even future opinion on Pay Per Click engines. The beginning of the book talks about the history of PPC, which is nice but not really meant for someone who wants to simply improve or get started with his or her PPC campaign. After you get past the intro pages, you get to the meat of the goodies. Of course the book delves deep into Google AdWords and Yahoo!'s Search Marketing (Overture), but it also goes into the 2nd and 3rd tier PPC engines and contextual components of PPC.
As you read through the book, you learn a great deal about the pros and cons of each PPC engine. They also provide detailed reviews of pay per click tools; management tools, tracking tools and research tools. This book is a no-brainer for anyone seriously using the PPC engines. For under $20, the coupons you get alone make it worthwhile.
For more information on this book, visit http://www.ppcbook.info/.