31. Tony Hsieh & Charles Best (tie)
Tony Hsieh & Charles Best (tie)
Tony Hsieh (l) and Charles Best
Hsieh: CEO, Zappos.com
Age: 38
Industry: Apparel

Hsieh still runs Zappos, but he's attained guru status when it comes to building workplaces: His "Delivering happiness" message is now the basis for a bestselling book and a company that exports his philosophy to giants like P&G and Hasbro.

Latest move: Investing in private jet outfit JetSuite.

Best: Founder, DonorsChoose.org
Age: 36
Industry: Nonprofit

Donations for Best's nonprofit, which raises funds for public school classrooms, are on track for $40 million this school year, nearly double from two years ago, and now total $90 million since 2000. Last year his gift card was among Oprah's "ultimate favorite things."

Last updated October 25 2011: 5:11 PM ET
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Ones to watch

In addition to Fortune's 40 Under 40 list, we're also keeping our eye on these 20 innovators, young guns from a wide range of industries and backgrounds.