Gates and Buffett's Giving Pledge didn't specify how people should give, just that they should. Tech entrepreneurs like Pierre and Pam Omidyar, perennials on the list, have tried enterprising donations, founding HopeLab to attempt to improve kids' health through technology. Zuckerberg's gift is unusual for reaching out to a public school system. If more and more of the Forbes 400 decide to join him, the next 15 years of the Slate 60 could look very different indeed. There's the quantitative measure: Fortune estimates that if all members of that list take the Giving Pledge, it could force a whopping $600 billion to nonprofit groups. But there's also a qualitative one: What if Buffett and Gates decide to push for better giving, not just more? Those sobering inequality numbers might not change—but who knows what could.
Click here to read a slide show of the top charitable donors of 2010.
Once again, Slate has partnered with the Chronicle of Philanthropy on this project. Special thanks go to Maria Di Mento, who compiled the list with help from Caroline Bermudez, Caroline Preston, Heather Joslyn and Sue LaLumia.