At another unrelated board that I am a member of, we had something similar.
It was called the Most Helpful Member contest. Here's how it worked. Everyone was able to send in nominations to the Administrator. Then, after a set period of time, he took all of the nominations and the moderators voted on them to come up with a list of top ten or so. Then, those members names were posted as finalists. Once again, everyone was allowed to send in their votes to the administrator.
All of the finalists received a custom signature file. It says something like 'Most Helpful Member finalist April 2003'. The winner received a similar signature file, however it says 'Most Helpful Member Winner April 2003'. The winner also got a 50% off coupon for any item in the eStore connected with the forum.
Maybe something like this can be modify to fit this board.
...chad...