Im not an expert but just collect best of web, while surfing & exploring.
CMS & Blog
drupal
www.drupal.org
joomla
www.joomla.com
ezpublish
www.ez.no
typo3
www.typo3.org
wordpress
www.wordpress.com
Shopping-Systems & Cart
OsCommerce
www.oscommerce.com
XTC
www.xt-commerce.com
Meganto
www.meganto.com
Drupal + Ubercart
Joomla + Virtuemart
Forum & Board-Systems
phpbb
www.phpbb.com
simplemachines
www.simplemachines.org
phorum
www.phorum.org
Tools & Utilities
phpmyadmin
www.phpmyadmin.net