Occasionally I'll let our 5-year-old earn money for doing additional, out-of-the-ordinary chores. Small amounts are sufficient for him - a quarter is usually all it takes to make him happy. I love the idea of using a chart like this one from My Love For Words is fabulous. This would be great for not only developing a good work ethic, but also learning financial responsibility!
See the Work for Hire Chore Chart.