When my kids were little I made my own mommy money from colored paper to use for chore incentives and rewards during the summer.
The kids earned the money by doing chores without being asked, being kind, honest, whatever! It worked well and our kids remember it better than any chore chart I ever made.
One of my daughters found THIS idea the other day from "The Idea Room." I think it's a brilliant incentive system for kids. Check it out.