* 2007 Evaluation of WYSIWYG editors: http://www.standards-schmandards.com/2007/wysiwyg-editor-tes...
* List of WYSIWYG rich text web editors from Genii Software Ltd: http://www.geniisoft.com/showcase.nsf/WebEditors
It's based on a partial implementation of the algorithm for parsing HTML specified in the HTML 5 draft - so it handles even really scary HTML from Word pasting, and spits of clean pretty printed and validating xhtml.
For our use we do put some pretty strict level on what markup people can include, though, so it might not serve for everybody.
As a Firefox plugin. Or use it the standard way.
Worked well enough for me, never felt the need to change
couple others I've had my eye on...
WYMeditor: http://files.wymeditor.org/wymeditor/trunk/src/examples/01-b...
and jWYSIWYG: http://code.google.com/p/jwysiwyg/