* When he plays, we all win
Dean Kamen, 51
CEO, Segway LLC

As a child, Dean Kamen was obsessed with spinning tops. In college he helped his brother, a doctor, by inventing a portable insulin pump. After dropping out, he started a medical equipment company and developed a portable dialysis machine. Then one slushy day in the late '80s he saw a man struggling to get his wheelchair up a curb. "I thought, Well, I could make a better wheelchair than this," Kamen recalls. And he did: The self-balancing iBOT not only climbs stairs, it zips along at a runner's pace and rises up on its rear wheels, elevating occupants so they're eye-to-eye with standing people. Last year Kamen made a splash with his Segway, a two-wheeled gyroscopically balanced scooter that he believes will revolutionize urban transportation. And these are just his latest inventions: Kamen holds more than 150 patents.

Running on empty: Currently, he is working on a generator for Third World nations that can run on anything from animal dung to butane to jet fuel. And the engine heat it produces powers a device that purifies water. "Polluted drinking water is one of the world's worst problems," he says.

On creativity: "People think I wake up and check out my calendar: '9:30: Invent something. 10:45: Get new idea. 11:30: See the world differently from other people.' If I could tell you how to innovate, I'd be sitting on a cloud throwing lightning bolts. I never have a final image of a project until I reach the point where I can say, 'That's pretty neat.' "

Use an interactive map to determine how much farther you can travel in 20 minutes via a Segway—or how long it will take to get to a specific location via a Segway.

* He made computers everybody-friendly
Alan Kay, 62
President, Viewpoints Research Institute

The Windows concept is so entrenched that we have forgotten what it took to work a computer before we could just point and click. Apple founder Steve Jobs was blown away when he glimpsed an early model of a Windows-like operating system on a visit to Kay's workshop at Xerox in 1979. "I thought it was the best thing I'd ever seen in my life," Jobs has said. (Xerox disagreed, so Jobs's copy, for Macintosh, was the first graphic user interface.) These days Kay aims his products at kids. His computer language, Squeak, enables youngsters to create programs from scratch. "The best way to predict the future," he has said, "is to invent it."

* She reinvented the rerun
Geraldine Laybourne, 55
Chairman and CEO, Oxygen Media

In 1985, when Laybourne was president of kid network Nickelodeon, she faced a post-bedtime programming conundrum. Her solution: Nick at Nite, a comfort-viewing selection of beloved reruns. Nickelodeon went from also-ran to known brand. What's more, in the cutthroat TV world, Laybourne was likable. Her Mother's Little Management Manifesto, rules for nurturing leadership, starts with: "It's not enough to know your customers. You also have to like them." In 1998 Laybourne noisily launched Oxygen Media, a TV-and-Internet network. It's still a work in progress, but Laybourne is confident. "I'm an optimist," she has said. "I'm a Norwegian and a textbook middle child. I have a high tolerance for struggling."

* He showed us tiny is beautiful
Leon Lederman, 80
Director Emeritus, Fermi National Accelerator Laboratory

The subatomic particles that physicist Lederman has discovered, such as the "beauty" quark, are so small they don't have a radius. Yet these fleeting specks are the building blocks of the universe, and Lederman's research earned him a 1988 Nobel Prize. After nearly three decades on the faculty of Columbia University, his new crusade is to reverse the order in which high school science is taught. Lederman advocates teaching physics first, then chemistry, and then biology, because they build upon each other. And he teaches high schoolers himself, at a public academy he helped found. "It's self-serving, really," he says. "Working with children is the secret to eternal youth."