Here. From Jesse Ezell: "I have put together a Xopus wrapper for .NET. Basically, it isolates you from having to know all the Xopus details: just drag, drop, and set the designer properties."
Xopus is an opensource browser based WYSIWYG xml / xsl based editor that works natively in IE 5.5+ / Mozilla 1.3+ / Netscape 7+. Pretty cool stuff.