Have multiple Santas (with your logo somewhere discreet, but noticeable, on their suit) going around the city offering gifts to passers-by. These gifts would candy canes, or a small, cheap, and relevant product to your company (a pencil sharpener if you were Office Max for example), each with an attached coupon code for an in-store purchase. Potential customers WILL tell their friends that story, and if they're already out and about, they'll probably stop by with their new coupon!