We’ve developed our own CMS with a front-end geared toward topical navigation and a back-end developed for users divided into departments. It’s open source and available at http://code.google.com/p/civic-cms/. It runs our website, http://bloomington.in.gov.
In the near future, we’re considering moving away from a deep section-based navigation and heading towards a shallower tag-based navigation.
If anyone is interested in this CMS or collaborative development, let me know!