ING Direct operates a fun site designed to teach kids about money called Planet Orange .
A lot of the content isn't exactly rocket science -- for example, it will take Ashley three months to save enough for a $100 skateboard if she saves $10 a week and only a little over a month if she saves $20 a week. But the anecdotes and illustrations are clever and it makes a handy way to introduce your child to the concept of budgeting.
My guess is the site would have the most appeal to kids in the 10-to-15 age range. But, come to think of it, saving $10 a week for a luxury purchase is an strategy I could use myself!