Content management systems have proliferated in recent years, and there are now many viable open source content management systems. The current big name CMSs include Joomla!, Drupal, and WordPress. Wikipedia has a large list of content management systems, and a open source CMSs. The following is a list of government websites, particularly local governments, that are operated with an open source content management system. These are sites that I have come by, I know there are many others. If you see any, please leave a comment or contact me.

Local Governments

States

White House

Federal

International

Others

Note: This is list is very limited so far. I have added to this list as I have come across sites using open source systems.

Note 2: WordPress has a showcase site (and specifically government sites here). Also, Drupal has a list of case studies of organizations that use Drupal.