Tony Hsieh was only 24 back in 1998 when he sold Link Exchange, his online advertising company, for an eye-popping $265 million. After a success like that, lots of people might be content to sit back and rest on their laurels.

Not Hsieh. Within a year, he was hard at work developing a new e-commerce Web site built on the novel concept of selling shoes online. Investors were skeptical – and wrong. The site, now known as Zappos.com, has watched its sales soar from $1.6 million in 1999 to $840 million in 2007, and it now boasts 9 million customers.