I shall be going as Hagrid. I have the costume, a stuffed baby Norbert, and a toy motorcycle. I'll be telling the kids that Snape shrnk my motorcycle. I also have one of those large spiders that have the air pump in them, so when you pump it, it looks like the spider is moving. After all - Hagrid does take care of magical creatures, so why not a spider?
I always answer the door in costume, and generally have fun wth the kids. Last year I was Green Lantern and I was asking if they'd seen Batman and Superman....
--*Rob