During the beta, I called my Death Knight Dingbat, only because it was the first thing that jumped to mind. But it was a little silly to hear the great knights of the Scourge ordering me around as Dingbat, so I'll probably go with something a little more threatening for the actual release: Marton? Erathor? Killahdk?
Whatever it is, now's probably a good time to check and make sure your name is free and get a toon in place before someone else takes it. And please: spare us from the "Darth" names. Nobody, including Arthas, wants those.