Best of Joomla!: Provides news, templates, tutorials and links

Drupal: Official homepage of the open source content management system. Offers documentation and the source for download and hosts a developers and community portal

Joomla!: Open Source Content Management System

Joomla24: Well-organized collection of free Joomla! templates

PHP-Nuke: Content management and portal solution featuring web-based administration, surveys, customizable blocks, modules and themes with multilanguage support. Requires PHP/MySQL. Requires paid registration for access to latest revision and some sections

PostNuke: PostNuke came to an official end in 2008