There are many good content management systems and one of the best is called Drupal.  A very good article by IBM comparing it to other similar systems  is here and is well worth reading if you are thnking of choosing a CMS.

It's worth noting that Mambo is very like Joomla. The latter grew out of the former after some political difficulties at Miro who funded the development of Mambo after which many of the developers left and set up Joomla. They both seem to be chugging along nicely and I'd recommend either.

I'd also like to add my 2p worth to the IBM article: I've always found it easier to create themes for  Mambo/Joomla than for Drupal. Also there are probably more out there for Mambo which can be used or edited. It is also possible to use one of the several commercial installers for any of this software so there comments on installation are valid but may not apply to everyone.