Age: 27
Company: Statcounter
Net Worth: $18 Million (estimated)
What's the Deal?: At the age of 16, Cullen founded StatCounter—a website that gives users the ability to monitor their site's analytics. The site currently has over 1.5 million users and attracts over 10 billion page views across its 3 million web site network. Judging by the math, it ain't hard to tell why this Irishman is raking in the green.