Drupal
The most popular CMS might be Wordpress or Joomla but I use Drupal. Drupal has won the Hall of Fame Award in the 2009 Open Source CMS Awards. Drupal previously won the 2007 and 2008 Best Overall Open Source CMS Award.
Separate Drupal Taxonomy Terms | 25 July 2011
theme user login form | 21 July 2011
Beginning Drupal modules | 2 July 2011
Drupal 7 differences | 2 July 2011
Drupal useful Modules | 16 November 2010
Drupal Core Modules | 16 November 2010
Drupal first thing | 06 November 2010
Retrieving Query Results | 18 November 2009