I personally prefer GM/Gamesmaster. DM/Dungeonmaster was what I was when I was 12 and it sounds a bit nerdy to my ears. Even though it invokes Genetically Modified, General Motors etc.
Terms like Referee and Judge don't cut it for me - they imply a role of aloof impartiality whereas being behind the screen involves more involvement than that. It's a very specific activity, mingling equal parts crowd control, creativity, challenge creating and impartial judgement, whereas a referee or a judge is rarely the one who creates the difficulties/opposition for players if you look at other areas where you would see such an individual.
More fancy pants terms, like Storyteller and Keeper of Arcane Knowledge - ehh. Faintly amusing at first, a bit up themselves at second glance.
Oh, and it's the Lazy *GM* series because of *grumble grumble* copyrighting. ...