If you care more about the mood and feel of your photos than the quality, these options are for you. We love disposable cameras for fun photo booths (buy unbranded versions in bulk on Ebay to cut down the cost and get snapping away).
The other option is a Polaroid or Instax camera. Both give you instant photo-booth-style photos that can be written on by your guests for an extrasweet touch. Make sure you buy enough film to get you through the night.