I got this idea from one of my brides, who got married earlier this year.
The name of the game is "I Spy", you will need to get some disposable cameras with flash for it to work well. Put a camera for each couple on the reception tables along with an "I Spy" shooting list. Make a list of the things they should photograph at the reception, to make it more fun. After your wedding, take these disposable cameras and pick your favorite photos, and make a thank you DVD to give to all your guests.
(Find Below An "I Spy" Card You Can Use)