Drupal Books

Book: 

Drupal 5 Themes: Create a new theme for your Drupal website with a clean layout and powerful CSS styling

Drupal 5 Themes, a 250 page paperback, gives people one thing they really want: a guide to creating a custom look for your site using css, some PHP code, images, and a little bit of effort.

It provides a bit of a review of existing themes and how to configure them for a custom look without any new code but also goes into how to create a completely custom theme.

Based on Packt Publiching's history we can only assume that it will be updated for future versions especially since theming has changed for Drupal6.

Long time contributors John VanDyk and Matt Westgate teamed up with support from lots of other community luminaries to produce the first book to really dive "under the hood" of Drupal. Pro Drupal Development, published in April of 2007 Pro Drupal Development (aka PDD) finally provided developers around the world with a thorough and well organized review of how to code and design your way to an amazing Drupal site.

At the time I read this book I considered myself to be a very knowledgable Drupal developer and I still learned a lot. The text is extremely well organized and detailed. The numerous flowcharts and diagrams really hammer home concepts that had been a fluffy cloud of disinformation before I read the book. This is "the bible" for any serious Drupal site admin, developer, and themer.

Book: 

Pro Drupal Development, Second Edition

Pro Drupal Development A 375 page paperback from APress was the first deep dive into Drupal.
Published in April 2007.
Paperback - also available as a pdf.
ISBN: 1590597559

Book: 

Building Powerful and Robust Websites with Drupal 6: Build your own professional blog, forum, portal or community website with Drupal 6

This 330 page paperback from PacktPublishing is not yet released, so the overview has to be brief. It is a follow on from their original book Building Websites with Drupal.

It is due out February 2008. Preorder Now.

Keep in mind I haven't read the book and am merely judging it based on what I know from the author's site.

I don't imagine many folks will be buying the book given that with shipping included you could probably wait for the 6.x version and not lose out on much. There is, however, a PDF Version available which might be worth it.