If you haven't yet: take a look at the Papercraft Star Blog. It's a hopin' place to be, and hosts great challenges based on not only sketches, but photos and other topics as well (like Simon Says!).
At Papercraft Star, the winner is chosen by the public, who can vote for whichever entry (link) they think is the best! We also have a winner, chosen by the judges and a Design Team member also wins based on people's choice as well.
I hope if you can, you will play with us, and if not- at least take a minute to check out the entries and vote!