Incentives and Positive Reinforcements

I've got a scholar dollar wall in my class and it's pretty neat. Students need to earn dollars by showing how scholarly they can be behavior wise and academically. The point system can be up to you. I have the students compete against each other to see who can get the most scholar dollars. The first person to reach 20 gets to bank their check. The points are erased from the board. That student gets to earn more dollars. On time to class? scholar dollar. Fastest five to class? scholar dollar Silently working and being productive? scholar dollar. so at the end of the marking period, the kid with the most scholar dollars gets 20 bucks. Initially I had each scholar dollar represent one real dollar. But I learned really quickly how broke that would make me :-) Just be sure to roll out the expectation. Any changes should be announced and not sprung upon the students. Which incentives do you use in your class?