Fountain of Youth: The Under 30 Hall of Fame

As a 19-year-old freshman at University of Texas at Austin, Dell borrowed $1,000 from his parents and started selling computer upgrade kits directly to customers. And a company was born. By his 40th birthday, he had netted $20 billion.

Cuban, an outspoken Texan, sold his software company Microsolutions to Compuserve for $6 million in 1990, and sold Broadcast.com to Yahoo five years later for $5.9 billion in stock. Today, he's best known for heckling the refs at Dallas Mavericks games, where he sits in the owner's chair. His latest venture is HDNet, a high-definition TV network.

Nicknamed "Kinko" because of his curly hair, he started Kinko’s in 1970 with a single copy machine, a converted taco stand, and a $5,000 loan. His idea to cater to college students worked -- 34 years later, the company sold for $2.4 billion.

A member of our inaugural 30 Under 30 list, this Zuckerberg launched the wildly popular social networking site in February 2004 with the help of some Harvard buddies. More than two-thirds of the school's students signed up in the first two weeks, and four years later, the site has more than 100 million users.

The Google guys met in 1995 as doctoral students at Stanford University and incorporated their search engine company in September 1998. After its initial public offering in 2004, Google was worth an estimated $23 billion. Today, its market cap is more than $136 billion, "Google" has become its a verb, and Brin and Page are two of the richest people in the world.

After scraping $8,000 together from friends and family, a 27-year-old Hefner launched Playboy in December 1953, featuring Marilyn Monroe on the magazine’s first cover. You know the rest.

Allen convinced Gates to drop out of Harvard to officially start Microsoft in 1976. After developing an operating system called MS-DOS for IBM in 1980, Microsoft became a major player in the computer software industry. The company powers most of the world's computers today. After 13 years as the reigning world's richest man, Gates recently slipped to No. 3, with a net worth estimated at a mere $58 billion. Allen, who owns the Seattle Seahawks, comes in at No. 41 with $16 billion.

This pair of Steves met as summer workers at Hewlett-Packard and started Apple in 1976 with $1,300 they pooled together after selling off personal possessions. They made the first prototypes of the Apple I in Jobs’ garage. Riding the massive success of the iPod and iTunes, Apple had more than $24 billion in revenue in 2007 -- with no signs of slowing down. Jobs remains at the helm.

These three former PayPal employees started YouTube, the Internet's most popular video-sharing site, in February 2005, after eBay's acquisition of PayPal netted Karim a few million dollars. A year and a half later, Google acquired YouTube for a deal worth $1.65 billion in stock.

With a $50,000 loan in hand, this native New Yorker started selling neckties under his Polo brand in 1967. Today, it's one of the most iconic labels in fashion.

As a student at Northeastern University in 1998, Fanning developed Napster, a breakthrough peer-to-peer file-sharing program, as a way to find and trade music. The service had more than 25 million users at its peak in 2001, and was shut down after a series of high-profile lawsuits, not before helping to spark the digital music revolution now dominated by Apple. Napster has since been rebranded and acquired by Roxio.

Rubin's NYU dorm room served as the incubator for this groundbreaking record label. Since then, Def Jam has released some of the most influential hip-hop records in history, including early releases by LL Cool J, Beastie Boys, and Public Enemy, and was later sold to Universal Music Group for a reported $100 million.

Aaron Patzer launched Mint.com as a user-friendly alternative to Quicken and other personal-finance software out there. Little did he know that just two years later, Intuit, which makes Quicken, would fork over $170 million for his website.