We're testing WYSIWYG editors, and we cannot see to make them work with asynchronous postbacks. We put the TextBox(/textarea) in the UpdatePanel and call a simple save to the DB, and all of our WYSIWYG toolbars disappear, leaving us with a bunch of HTML in textboxes.
This is the one we've been working to implement: nicedit.com/ We have found that CuteEditor works with asynch. postbacks, but we've had so many problems with it, we're scrapping it entirely.
Those are just two examples, but we've tried a number of others, including TinyMCE. What is causing this to mess up on the AJAX call?
Edit - I agree with Thomas that it has something to do with the WYSIWYG editor running javascript during the "onLoad" event. Unfortunately the UpdatePanel request kills that and doesn't re-render the WYSIWYG editors. So other people can experiment, here's another SO question that hooks into the client-side PageLoad event.
Edit 2 - Ultimately I ended up binding the WYSIWYG load/render event to the element's onfocus event using jQuery.