List of these ebooks is below.
Apress - Building Online Communities with Drupal, phpBB, and WordPress (2006).pdf
Apress - Pro Drupal Development 2nd Edition (2008).pdf
Drupal 6, Ultimate Community Site Guide (2009).pdf
O'Reilly - Using Drupal (2009).pdf
Packt - Building powerful and robust websites with Drupal 6 (2008).pdf
Packt - Drupal 5 Themes (2007).pdf
Packt - Drupal 5 Views Recipes (2009).pdf
Packt - Drupal 6 Content Administration (2009).pdf
Packt - Drupal 6 javascript and jQuery (2009).pdf
Packt - Drupal 6 Search Engine Optimization (2009).pdf
Packt - Drupal 6 Site Blueprints (2009).pdf
Packt - Drupal 6 Site Builder Solutions (2008).pdf
Packt - Drupal 6 Social Networking (2009).pdf
Packt - Drupal 6 Themes (2008).pdf
Packt - Drupal for Education and E-Learning (2008).pdf
Packt - Drupal Multimedia (2008).pdf
Packt - Drupal, Creating Blogs, Forums, Portals and Community Websites (2006).pdf
Packt - Flash with Drupal (2009).pdf
Packt - Learning Drupal 6 Module Development (2008).pdf
Packt - Selling Online with Drupal e-Commerce (2008).pdf
Prentice Hall - Front End Drupal, Designing, Theming and Scripting (2009).pdf
Wiley - Cracking Drupal, A Drop in the Bucket (2009).pdf
Wrox - Leveraging Drupal, Getting Your Site Done Right (2009).pdf