If you haven't read Daniel Pink's book Drive, you should. Daniel Pink suggests that the "carrot and stick" approach to rewarding good behavior / work ethic isn't effective. He says that allowing people to be self-directed and creative is more powerful and motivating than any monetary bonus. How does this apply to your classroom and your students? Watch this video from RSAnimate and listen for the part about Atlassian Software.
What if for one whole day your students could work with WHOEVER they wanted on WHATEVER they wanted as long as they showed a final product at the end. I think you would find that they are much more productive than we could ever dream when they are intrinsically motivated! Josh Stumpenhorst wrote about "Innovation Day" on his blog - an idea that I think is out of this world! I think we should start a movement to create a statewide (or heck, nationwide!) Innovation Day to get our kids THINKING and CREATING and COLLABORATING! Who's with me?! :)