many of you may know about this, but i thought it is a good share. if you have a html page, you can use cushycms and it will turn a html page into a content management system that will allow you or your clients to edit/add content without even seeing any of the code. i think it really rocks and they have the free service(does everything above) and then the paid service if you want to add special editors or sub domains for the client. to understand it best, watch the video on their site.
Not sure if this is good for clients if you want to offer a professional web design service, surely better to create your own CMS system. Does not take a lot, either php or asp will do;-)
Your clients will love you for showing them this as it saves them money, but you still have to make a living right?
The market I'm thinking of is those clients who can't afford a new web site and are still using html. This way you actually opened a new up market and new product to offer. I mean set up is what, maybe 30 min?