WYSIWYG Cross Browser Editor
I came across this pretty nifty in-page HTML editor tonight called openWYSIWYG. The claim it was the ultimate cross-browser editor, but it didn't support Apple's Safari browser. Go figure. I liked it though. It's small and light and so far it seems like you can modify it fairly easily. Compared to FCKEditor or TinyMCE, which seems like brain surgery whenever I poke around in their code.
Well as of tonight, the Safari limitation has been changed. I have successfully modified the source to allow my brethren to enjoy it as well.