Yes, thanks for sharing that TM. Sorry for requiring the older binary, I think I still have the sources somewhere if anyone wants to build it themselves.
As soon as .Net Framework 4 hits beta 2 I will be re-examining the current builds of AvalonEdit (which require 4). I stopped work on code completion because of some limitations (perceived/real yet to be determined).
Another option would be Actipro SyntaxEditor, but it doesn't come cheap and is still in beta.