I read an article that was quite useful about teaching kids how to wisely spend money.  It talked about them having lemonade stands, etc.  My kids and neighbor kids setup a lemonade stand about a month ago and it was the cutest thing.  They actually sold all their stock and they split up the money evenly between 7 of them at the end of the afternoon.  Here is a link to the article that I read - it's a slideshow and I thought interesting, although a lot of it common sense.

Inc.com