From Six Revisions:
WordPress provides designers utmost control over a theme - resulting in unprecented flexibility in the layout and design direction he or she can take. WordPress - in the title - is inside parentheses because the designs you’ll see below are wonderful designs despite of the publishing platform they use (which just so happens to be WordPress).
In this collection, you’ll find some (45 of them to be exact) of the most attractive, creative designs by talented designers who push the limits of WordPress theming and raise the bar for the rest of us.
See the List
WordPress All-in-One For Dummies
Build Your Own Wicked WordPress Themes
WordPress 24-Hour Trainer: Watch, Read, and Learn How to Create and Customize WordPress Sites (Book & DVD)