RadEditor does provide great functionality, but unfortunately you cannot use it in a Silverlight application. RadRichTextBox is the closest option you could get. It is a rather new control and as such it may not have all the capabilities RadEditor offers, but it is evolving pretty impressively and with Q3 on the way, it's becoming a full-featured rich text editor. In this way of thinking, if you have any suggestions on capabilities you are looking for and not finding in it, we would be happy to hear from you.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items