I've gotta go with the white t-shirt party on this one. Everyone wears a plain white t-shirt that they don't care about anymore and they bring a marker. Write whatever you want on whoever you want and by the end of the night you wouldn't believe how many people you've met, and you have proof of it the next day. The t-shirts make great souveniers, too...
Liz
Delta Delta Delta
Theta Sigma