I have been using the FCK Text Editor for almost 2 years, and finally codeplex have come out with a new ASP.NET AJAX Rich Text Editor.

Featurewise it has all the funtionality of FCKeditor; I think tha performance it not upto the previous one, but who cares the AJAX makes it all the more usable.

And it also supports multiple languages. Here is the code plex link.