WordPress

Addison-Wesley

WordPress In Depth
WordPress In Depth

PeachPit

WordPress: Visual QuickStart Guide
WordPress
Web Designer's Guide to WordPress: Plan, Theme, Build, Launch
Web Designer's Guide to WordPress

Apress

Beginning WordPress 3
Beginning WordPress 3
WordPress for Web Developers
WordPress for Web Developers

SitePoint

The WordPress Anthology
The WordPress Anthology
Build Your Own Wicked Wordpress Themes
Build Your Own Wicked Wordpress Themes