How To Add a Rich Text Box To Your ASP.net - C# -Web Site

You can use FCKEditor for your purpose.

I found a good link & like to share with.

http://www.codedigest.com/Articles/ASPNET/208_Integrating_FCKeditor_in_ASPNet_Websites_%E2%80%93_Part_1.aspx

http://www.codedigest.com/Articles/ASPNET/217_Integrating_FCKeditor_in_ASPNet_Websites_%E2%80%93_Part_2.aspx