1. Pet Battle Tourny - MoP will be out by then and Blizzard said the retail expansion will not be required to use the Pet Battle System. You might put in a stipulation that at least one of each contestant's three pet team be "spooky" themed.
2. Zombie Invasion - This was an awesome event from last year and definitely needs to be done again even bigger and better!
And if I might suggest a return of Azerothian Ghost Stories competition, with rule stipulations that all entries must be macroed and no more than 5 minutes duration so we can keep it moving along.