Pierre & Pam Omidyar

Cause: Enabling the economic self-empowerment of individuals. In 2004 the Omidyars started Omidyar Network, which allows the microfinance sector to access private-capital markets in for-profit and not-for-profit ventures. The Network operates by helping connect people who want to give with those in need.

Impact: Since 1998, the Omidyars, both 39, have donated more than $623 million, about $66 million in 2006 alone.