Open source CMS

I personally am excited about the development of Adobe's In-context Editing (ICE)

It brings all of the editable featured most clients want out of their content management system (CMS)

However there may be times when your needs will out grow what ICE can do...

Here's a list of some open source CMS's to consider

http://www.dreamcss.com/2009/08/9-open-source-content-management.html