A great free editor is TMedit, It's super easy to use and is bug-free.
Another option is JCE (Joomla Content Editor). It's got advanced image/media and file handling, plugin support, and an admin interface that the developer can play around with. The only minus is that it can be a bit of a nuisance to install. (Start with the admin component first, then install the editor mambot before moving on to the plugins). It has some bugs but you may be able to make it work.