This site runs WordPress. WordPress is a content management system which I find very accessible for humans to operate. There are lots of CMS offerings available, and WordPress is just one option, but so far it's proven to be the most usable for our clients.
Quite a few of our customer sites are based on WordPress now, including:
We have built a number of plugins for client-specific tasks (eg for the Green Party during their 2005 electoral campaign, or for online retail of vehicle reviews for the Dog and Lemon Guide). WordPress is well coded and allows easy extension, which saves our customers time and money in development.
There are some free WordPress plugins available for your use, too ... enjoy!