Arnold Jagt has written up a how-to for getting the popular FCKEditor to work with ExpressionEngine. This will basically allow you to switch to a WYSIWYG editor for entering posts into ExpressionEngine merely by double clicking on the textarea field you want to use it on. Implementation will require the hacking of a couple of source files, but if you’ve been looking for a solution like this the changes required appear to be rather minimal and the editor is pretty robust.