Liferay is an Enterprise Content Management System focused on corporations. It is a direct competitor for SharePoint (by Microsoft). I believe that Liferay is best suited for a corporate portal building.

Joomla! is a great CMS with a long dramatic history rooting in Mambo. This one along with the Drupal and the Wordpress forms a "Big Three" of the Opens Source CMS world. I'd say that Joomla! is just huge. It has good integration modules with many other Open Source products. And it's quite easy to start with for an end user.

Probably, it's the #1 CMS in the world of Open Source CMS/CMF solutions. Huge user base, many awards, compact code, huge number of third-party modules, all these are some facts about the Drupal CMS.

As a former programmer, I'm just amazed with this framework simplicity and flexibility. Its architecture concept is beautiful and solid. You really do not have to change anything in the code provided in distribution to add functionality or even to fix some bugs.