I updated dtutorials.com - Drupal tutorials aggregator and added Drupal books section there. All books are tagged with compatible Drupal version. Overall, we have 18 drupal books right now. The most notable and recommended books are:
Feel free to suggest missing books (starting from D6 version). P.S. Guys, I do really need your assistance with promoting dtutorials.com, if we make it more popular it will aggregate every peace of useful Drupal content. Please add links to Drupal tutorials plus if you have a blog or simple social bookmark account, add http://dtutorials.com with an anchor "Drupal tutorials". Spend a five minutes of your time to add something useful to dtutorials.com site. Thank you very much in advance, I hope together we will succeed.