Just got a tip-off about this rather neat idea: CushyCMS is a third-party, hosted CMS for your own (or your clients’) sites. It works by embedding class definitions in editable elements, and then using FTP (you have to supply FTP details for your own host) to make changes.
The CMS software itself is very simple easy-to-use, and I think would be ideal for clients who don’t have much technical experience. It’s free, too, although it’s unclear if/how that will change.
Check out the video presentation to see how it works.