Pro Drupal Development Second Edition
Selwyn's review: The first edition has to be one of the most useful Drupal books for me. I am a programmer so don't even bother with this one if you aren't interested in hunkering down with your favorite editor and coding. Really gets into the heart of Drupal. I am ordering this second edition of "Pro Drupal Development." If it is anywhere near as useful as the first one, it is going to be seriously marred and marked in with folded over pages and tons of stickies hanging off essential pages.
The first edition did have quite a few minor typos and things which added to the challenge of learning Drupal coding but that seemed to help as it sent me over to www.drupal.org and got me searching.