There are actually several excellent FOSS CMS systems out there, any of which would probably be fine for your client.
On DreamHost, I have used:
Both Joomla! and WordPRess are available on Dreamhost as “one-click” installs and, while WordPress began life as (and actually still is) primarily a blog platform, it’s current version’s “pages” feature makes it highly usable as a CMS.
You can visit opensourcecms to actually demo these, and many other FOSS CMSs.