Recently Lutz Roeder took Documentor off his list of .NET Tools, and I was bummed. Mark Miller and I have been talking about doing a documentation plugin for CodeRush. I was working on one that did MSDN style help, and Mark did one that was more stylized and painted directly over the XML Comments.
However, Travis Illig (who works with me) in his wisdom, emailed Lutz and got the source to the now defunct Documentor. He then updated Documentor and implemented it as a drop-in CodeRush PlugIn!
He adds a new VS.NET ToolWindow that will render the XML comment that your cursor is currently on as MSDN-Style Help. As you type, about a second later (when CodeRush parses next), the ToolWindow is updated.
This is nice if you're using NDoc to generate your MSDN-style CHM Help files and you want to use some of the more advanced (and useful) C# XML Comment tags, but are not sure how it's going to turn out.