#6 Garrett Camp, cofounder Uber, Stumbleupon

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Garrett co-founded StumbleUpon in 2001 in Canada, and moved the company to San Francisco in 2006. In 2007, Camp sold the company to eBay for 75 million dollars. Camp was able to buy the company back for a reported 29 million dollars, in 2009, and revamp it to where it sits today. As of April 2012 StumbleUpon has over 25 million registered users. In May 2012 he stepped down as a CEO, but continues as Stumbleupon's Chairman.

He's also cofounder and chairman of Uber, the car service that's turning the ancient taxi-cab business on its ear.

#5 Robby Walker, cofounder, Cue

Robby Walker's first company, Zenter, was snapped up by Google in 2007 before it even launched. Zenter, an online "PowerPoint killer" app became part of Google's Apps presentation software. Then Walker stuck around Google for three years improving the presentation software used by Apps.

He's now working on a cool Ycombinator startup called Cue launched with a teenage cofounder, Daniel Gross. Cue is a mobile app that turns all of your email, calendars, social media streams into a manageable day planner.

Like Gross, Walker was a child coding prodigy. He began attending college at age 9, earned a doctorate by 22 and sold Zenter to Google at the ripe old age of 23.

Also Read: Unknown Facts About 15 Richest Tech Titans and  15 Richest Internet Entrepreneurs Of All Time