One of the best things we did for the wedding was definitely the photobooth. It was an absolute hit with all the guests, young and old.
We hung a line made of bakers twine for the photos to be clipped to so everyone could look at them and the guests took them home with them at the end of the evening. You are also left with them on file.
We used Sparkbooth and a Canon instant printer I got off Ebay for $50. We had some trouble setting it up because Adam had just got a new laptop and the program wouldn't work with Windows 7- so at the eleventh hour we were racing around trying to find a laptop to use! Other than that it was quite simple to set up- but I'd recommend doing the set up earlier than the day before!
We used a simple backdrop and left a few props for people to play with. The biggest problem we had was keeping the kids off it... we literally had to fight them for a turn!