At our costume contest this year, each costumed guest will have their picture taken with a polaroid camera, and then the pic will be posted on the board with their name written under their picture. We use the "ballot" method, and I have pre-made ballots with each category on them, and each category has a different colored paper. I've got a shoe box covered in really cool Halloween paper, and it's completely covered so that it has to be opened with a letter opener along the sides when it's time to count the votes. That way no one can sneek a peak or tamper with the votes (I live in Florida, after all

We are doing 6 categories: Best male, female, boy, girl, funniest and most unique to the theme. Each winner will get a trophy and a prize basket I've assembled with age/gender appropriate prizes. I post the rules next to the ballot box, and mainly, no one is allowed to vote for me (the host) or themselves.