Viral Marketing Tool

I am looking for an off the wall solution that will enable Viral Marketing. A flash game comes to mind. viral marketing Definition viral marketing Marketing phenomenon that facilitates and encourages people to pass along a marketing message. Information Viral marketing depends on a high pass-along rate from person to person. If a large percentage of recipients forward something to a large number of friends, the overall growth snowballs very quickly. If the pass-along numbers get too low, the overall growth quickly fizzles. The site to promote is a shopping portal. The requirements of this job are purposely left vague to allow for creativity. If the final solution performs well, there is a great deal of other work that can be gained.