There are many of the WordPress books I know about.
Some of them: Professional WordPress:
Design and Development (Brad Williams, David Damstra, Hal Stern),
Web Designer’s Guide to WordPress(Jesse Friedman),
Building WordPress Themes From Scratch (Joe Casabona),
WordPress for Dummies (Lisa Sabin-Wilson)..
I’ve read already “Digging Into WordPress” (Jeff Starr, Chris Coyier).
This book is in clear, easy-to-read language also gives you the tools and knowledge to tap WordPress’ potential and take your site to the next level.
I’ve found soooo amazing and helpful book “Teach Yourself WordPress 3 in 10 Minutes” (Chuck Tomasi, Kreg Steppe), that book gives you straightforward, practical answers when you need fast results. By working through its 10-minute lessons, you’ll learn everything you need to build great blogs with WordPress and WordPress.org, and reach any audience by web browser, RSS, or cell phone.