I also love the mad scientist lab or room. There are so many things that can be used. The Dollar tree grow things found in the toy section are great. They have zombie limbs at the moment, alligators, snakes, etc. During Halloween season they carry some cool brains, hands, feet.
I would also have something witchy. It is not Halloween without witch things---IMHO. Maybe just your kitchen area. I always toss some of the Dollar Tree body parts--brains, heart, ears, fingers, etc. into pans on the stove top or into a big soup pan. Make some potion bottles and drape some DT creepy cloth over the cabinets.
Vampire Room would also be cool. I am loving the Vampire Killing Kits or Werewolf Killing Kits. I posted some links in the past day or so to some really cheap scene setters and things for vampires.
Bats and/or spiders also make a great room. You can even make bats to hang from the ceiling.