The Telerik XAML SDK repository provides additional demos for most of the Telerik UI for Silverlight controls. The examples demonstrate many specific user case scenarios, that might be really helpful. In this article you can find the complete list of all SDK examples for RadRichTextBox.
You can also check the SDK Samples Browser that provides a more convenient approach in exploring and executing the examples in the Telerik XAML SDK repository. The SDK Samples Browser application is available for download from this link.