In fact, we are using these applications for our portal and marketing site:

WordPress
The most common of all blogging software, WordPress scales from simplicity for novice users to dense with community driven plugins for more advanced users.  It is also open-source which makes the price just right.

http://wordpress.org/

Geeklog
Another content management system that focuses more on security as opposed to extended functionality or fancy bells & whistles.  This one is also open-source and still in active development.

http://www.geeklog.net/

TikiWiki
This is a full service content management system that also has support for wiki’s, blogs, forums, image galleries, etc. all from the same application.  It is open-source and development continues at a furious pace with new code changes committed on average every 2 hours.

http://info.tikiwiki.org/tiki-index.php

RequestTracker
This is an open-source ticketing system that is one of the most widely used on the web.  Written in perl and under development since 1996 this free application helps manage workflow and can be setup to function entirely via email messages.

http://bestpractical.com/rt/