Pierre Omidyar and Matt Bannick, Omidyar NetworkAfter starting and later shuttering his own nonprofit, eBay founder Omidyar (left) became convinced that using business tools was a better way to solve social problems. So in 2004 he launched Omidyar Network, an organization that pairs a traditional foundation with a for-profit venture fund. Matt Bannick, the former president of eBay International, runs the firm, which has already made $120 million in investments.
They're supporting nonprofits like Donorschoose.org, which gives kids school supplies, as well as enterprises like Prosper.com, a consumer lending site, helping Omidyar Network to become as big a name in the social sector as eBay is in the dot-com world.
Last updated January 11 2008: 5:15 PM ET