I love the slug costume. I may steal that one!
We usually go to Halloween parties with a large contingent of gay men. They have all the best costumes!
The year that the Statue of Liberty had its extreme makeover (76?) a friend of mine went to a party as the statue. He was very tall, and he surrounded himself with scaffolding. Very impressive!
Other favorites I've seen are a pair of high heels, with the guys' bodies as the heels and the huge shoes in rollers in front of them, the "girl in the radiator" from "Eraserhead", a male and female plug and socket (when they plugged in, bulbs lit up on top of their heads), a guy dressed as a swami on rollerblades surrounded by a small carpet that stuck straight out on all sides and little fake legs crossed on top so it looked like he was on a flying carpet, a flasher with a huge fake penis that contained a canister of "Silly String" (you can just imagine...), a handsome black man dressed in jockey gear and carrying a lantern, posing as a lawn jockey. The list goes on...
CNN also has good parties---you dress as a news story. Usually they're pretty sick (wet stewardesses when there's an aircrash, etc.) but those people are under a lot of stress working there, so it's a way to make light, for a day, of the grim stuff they cover. I imagine there will be quite a few Amish in the crowd.