FreeTextBox HTML Editor
The most-used free ASP.NET WYSIWYG HTML editor featured in
open source and commerical projects. Just drop FreeTextbox.dll in your
/bin/ folder, change
<asp:Textbox /> to
<FTB:FreeTextbox />, and you're done.
FreeTextBox is no longer being actively developed and both the control and source are free to download.