Documentation:
Drupal handbooks
http://drupal.org/handbooks
The Drupal handbooks offer a complete reference for those interested in Drupal, both novice and experienced Drupal administrators, Drupal users and Drupal developers.
 
Drupal for Information Architects: an overview of configurability
http://drupal.org/node/49297
Drupal provides several ways to structure information through layout, navigation, styling, and applications. This articles explains some of those options
 
Drupal Dojo
http://drupaldojo.com
Rich online lessons and documentation maintained by a passionate community committed to transferring Drupal skills and knowledge
 

 

 
Useful Links:

 

 
Training:
Drupal training page at drupal.org
http://drupal.org/node/26441
Limited discussion about training on Drupal
 
DrupalCamp
http://drupal-camp.org
Meatspace Drupal Training events
 
Lullabot
http://www.lullabot.com/
Lullabot provides consulting and training for Drupal and other open source software.
 
NTEN Drupal Resource List
http://groups.nten.org/message.htm?mode=view&hi...
Discussion thread listing resources for those starting with Drupal from scratch.
 
Intro to Drupal Video
http://chasesagum.com/an-intro-video-to-drupal
ChaseSagum.com showcases a 20 minute intro to Drupal for the uninitiated.