Just as you cannot be clueless regarding open source, you cannot be clueless regarding the iterative and incremental approach. This is the master. Listen. It is to method and process what the Cathedral and the Bazaar is to open source.

The Bible. The internals of Drupal. Indispensable Come back to it again and again. When a new edition comes out, buy that. If you can only afford one Drupal book, buy this one, then stop drinking beer for a week and then buy mine, Leveraging Drupal.

This book is a stroke of genius, and is to theming and Drupal presentation what my book, modestly speaking, attempts to be, for Drupal architecture and site building in general. It has it all, theory and "hands on".

Fundamental. Absolutely necessary.

You need to know your way around image editing. You need to be able to receive work done by graphic artists and make use of it. Use Gimp. Use Open Source. Use Gimp.

You know. You program. Do the same thing you always do, but now in PHP. Simple. Or, you don't program in anything. Learn how in PHP! A cookbook!

Whether you use Git or SVN for version control and as part of your distribution and deployment methods (adopting the wise method of working on a test site and then deploying to a production site), you need a book.

Even though Drupal is built on procedural PHP (although more and more of its modules are moving to OOP, like the Views 2 module), it is smart in OOP ways. This book explained to me what the object oriented paradigm is all about, as a way of solving problems, as the best way people have ever figured out how to divide and conquer complex problems, including your client's requirements.

I love this book. It's another one that brings it all together, a profound and practical resource.