Andrew Black & Edward Wray

Who says finance can't be fun? Certainly not Andrew Black and Edward Wray, ex-traders who turned their flair for the stock market into a flourishing Internet betting business. Black, 42, who also has been a software programmer and a professional card player, came up with the idea of peer-to-peer gambling site Betfair.com in the late '90s. "I worked up a prototype in my spare time and was confident it would attract punters [gamblers] -- because I am one," he says. Persuading Wray, who had spent eight years trading at JPMorgan Chase & Co. (JPM ), to join him was easy. "Betfair is just like a stock market, but more fun," says Wray, 37. "Now I can't imagine doing anything else."

Indeed, Betfair operates more like an electronic stock exchange than a traditional bookmaker. Just as NASDAQ matches bids and offers for stocks, Betfair pairs bets between gamblers on sporting events. Betfair doesn't take on any risk by setting the odds. It makes its money on commissions, which run 2% to 5% depending on the size and frequency of the winners' bets. Players set up a Betfair account and put down enough money to cover a bet's worst-case scenario. The system automatically collects from the loser and pays the winner.