TinyMCE, or Tiny Moxie Code Editor, is a WYSIWYG textarea replacement written in Javascript. I am actually very impressed with it. After using HTMLArea and a few others in the past which never seemed to work exactly right in Firefox, it seems this one does pull it off. Judging from the Compatibility Chart, their system works in most of the good browsers of today.

I've just integrated it into the management interface of my CMS simply by copying over the js files to the CMS directory and 6 lines of code! It is very easy to configure the editor using simple parameters in the init function of the code. Very, very good.