For big crowds, especially co-ed ones, try swinging away from convention. Pick an evening and rent the back room of a bar. Make sure there's at least one pool table and a dart board and let the party play. If the bride and groom are sports fans, you can even watch a game during the shower. It's a party that puts everyone at ease (and since it's at a bar, no one has to clean up afterwards).
Gift Suggestion: Kitchen Juicer (for the morning after)