This is an interesting topic! One type of extrinsic reward that can have positive effects in the classroom is the "token economy" system. Students who complete certain activities or perform appropriate behaviors can earn tokens which can then be traded in for tangible reward items or activities the students enjoy, such as being allowed time to play computer games. This can also be used in reverse fashion, where students start with a given number of tokens and have them taken away for negative performance. This has the benefit of being relevant to real-world situations, where employees earn incentives, or suffer adverse consequences at their jobs for inadequate performance.
