Colin M. Saunders has used web services to create two unique stock market type games. The first, AlexaDex, is a market-style game based on website values. You sign-up and start out with $10K of funny money you can invest in URLs. The value of any given URL goes up or down over time based on Alexa's rankings for that site's current reach.
Or, perhaps you'd prefer to spend idle time with Colin's amazdaq. As the he says on the site "amazdaq is a stock-market -type game, using amazon.com sales ranks as prices. To play, create an amazon.com listmania list, then copy and paste your list's URL into the box below. Add products to your list before they become popular, remove them when they reach their peak!"