I have found a really great book for those who want to do Drupal development from O’Reilly.Programmer’s Guide to Drupal. This isn’t really a book for those who want to lhaveearn PHP though. It’s for those who are already comfortable with coding and want to apply those skills to Drupal.
What this book does really well is to show you when to start writing your own code and when not to. It also recommends that a novice Drupal developer learn to build sites in Drupal without any custom coding at all in the beginning. With something like 24,000 modules out there, there is always a good chance that someone has already written code for the very purpose you have. Or that judicious use of core modules will allow you to get where you need to be.
Check this book out: it is AWESOME!