Joomla! is a terrific content management system.
- Installation is straightforward
- Websites are easy to maintain
- Joomla has lots of built-in features
- Lots of extensions available for things like video display, image galleries, event management, tagging, document management, etc.
- Many free and commercial templates are available to make your website attractive
Main Joomla! website: http://www.joomla.org
Joomla Support forums: http://forum.joomla.org/