Flavorwire has a nice gallery of historical Halloween costumes, which, by their very nature are much creepier than any contemporary costume could ever hope to be.
"We scoured the web for the wildest, weirdest costumes of yesteryear, and came up with everything from toadstools to telephones - and one guy in 'fancy dress as a side of bacon.'"
If you're hoping to find inspiration for this year's outfit though, you're bang out of luck. Evidently, the revellers of yesteryear had a lot more time on their hands and a lot more access to to high-quality natural fabrics. Special mention to the group of children with burlap sacks on their faces. Low effort, but very, very scary.