The following are some HTML Editors for ASP.NET providing "Rich Text box" functionality and are definitely worth a try.
FreeTextBox >> http://freetextbox.com/
FCKEditor >> http://www.fckeditor.net/
TinyMCE >> http://tinymce.moxiecode.com/
This list is by no means complete. There are a couple of other Rich Text editors on the ASP.net control gallery like the Telerik RadEditor. Be sure not to miss them! If you favor other editors just drop a line in the comments. Thanks!