"Rob your neighbor" is always fun. Say there are 20 people in a group...you write the #'s 1-20 on separate pieces of paper and have each person choose a number out of the hat. The first person (#1) chooses a gift and unwraps it. The next person (#2) can either choose a new gift to unwrap, or steal #1's gift. If he/she steals, then #1 gets to choose a new gift. Kinda hard to explain but I'm sure you've heard of it. We also make a rule that each gift can only be stolen 3 times. We play it every year w/a group of 40-45 and it's the most fun of the evening.