which could be a bit complicated to deploy. Well, there is always the trade-off btw complexity & functionality.
I think Drupal and Joomla are the best open source CMS out there (Plone is too heavy for regular servers now). Drupal probably offers more flexibilities and better admin interface. They both have large user bases and plenty of code extensions. And you can always tweak the php stuffs yourself.
If you just look for a blog system, Wordpress and others might be a better place to look at.

More at:
drupal.org
drupalchina.org