Check out a free online stock market game at UpDown. I have another article up over at Freewaregenius giving the inside scoop on this site and what a stock exchange simulator means. You can basically think of this as Fantasy football meets the stock market. You invest virtual money and make fictional trades to turn the virtual million dollars that you start off with grow.
Check out all the details and all that UpDown has to offer in the full Freewaregenius article.