Good question. It can range from very simple, less complex editing like CushyCMS or Surreal CMS, to mid-range CMS solutions like Concrete, to enterprise solutions like Expression Engine, SharePoint, etc. You might want to try symphony-cms.com

I'd say GetSimpleCMS (get-simple.info ) for simple sites; Wordpress for more complex ones (see bit.ly ) and maybe Drupal for really complex sites.

I personally prefer sharepoint. I got my digital  certificate through sharepoint - it's the best out there in my opinion.