Keywords

Gravestones
Zombies
Giant spiders
Bat wings
Spider webs
Witches
Cauldron
Gargoyles 
Coffins
"Enter At Your Own Risk"
Snakes
Full moon
Scarecrow
Skeletons
Tree moss
Bats
Jack-o-lanterns
Ravens
Chains
Wrought iron fence
Noose
Skulls
Pumpkin patch
Archway
Tree branches
"Bloody" clothing, shoes
Ghosts
Surgery/autopsy

Bringing it to life (or un-death)

Rear projection
Zip line
Animatronic
Black lights
Sound effects
Fog machines

Decorating themes

Graveyard
Haunted house
Frankenstein's lab (Jacob's ladder, knife switches)
Surgery/autopsy (similar to the above, but calls for different props)
Pirate ship
Sci-fi (e.g., '50s ray guns, astronauts, vinyl suits)
Torture chamber (a la Hellraiser)