Joomla, Drupal, Wordpress, or ExpressionEngine?
pavs: Wordpress. I don't know of anything you can't do with wordpress that you can do with other mentioned CMS here. Wordpress is extremely flexible with the largest user base and community support (among the CMS mentioned here). Depending on your speed of learning you can take it apart and put it back in a matter of days and can virtually do anything you could possible want with it.