RadEditor (Telerik). AJAX-enabled.
WebHtmlEditor (Infragistics). Part of the NetAdvantage for ASP.NET suite (I think).
Cute Editor (CuteSoft)
FreeTextBox (FreeTextBox.com). Free for basic edition. Source code available (for a price).
Peter's Textboxes (Peter Blum). Suite of enhanced text box controls.
UltimateEditor (Karamasoft)
Asbru Web Content Editor (Asbru)
ASP.Net XHTML WYSIWYG Editor (MoreNet)
AspLib Component library (Astron Digital). Includes a WYSIWYG editor, among other things.
ASPxHtmlEditor Suite (DevExpress)
ComponentArt Editor for ASP.NET AJAX. (ComponentArt)
EditLive! (Ephox)
eWebEditor (eWebEditor)
eWebEditPro (Ektron)
InnovaStudio WYSIWYG Editor (InnovaStudio)
FCKeditor (FredCK.com)
Html TextBox (ActiveUp). Part of the ActiveUp.WebControls suite.
Obout Editor for ASP.NET (Obout)
pinEdit (Pintexx)
PowerWEB TextBox for ASP.NET (Dart).
RichTextBox (aspControls)
RichTextEditor (Syncfusion)
RTE ASP.NET Control. Released under an MS-PL license on CodePlex. Includes source.
SmartText (Z-SoftNet)
soEditor (SiteObjects).
SPAW Editor v.2 (Solmetra)
TinyMCE (Moxiecode). JavaScript based; open source under LGPL.
Ueditor (Yardi). Free; source and restribution for a price.
WebHtmlEdit Control (JitBit Software)
collected by Joe Stagner at http://blogs.msdn.com/joestagner/archive/2008/06/18/why-would-you-want-to-write-your-own-wysiwyg-editor.aspx
