The largest American charitable contributions of the past year.

Sometime in the past decade or so, America woke up and realized it had become one of the more unequal societies on Earth. As masterfully described by Slate's Timothy Noah in his series "The United States of Inequality," the country's have-everythings have sprinted away from the mere haves or the have-nots in the past 30 years. Inequality is worse now than in the time of the Rockefellers or the Carnegies, with the top 10 percent of earners taking in more than 40 percent of income. The top one-tenth of 1 percent alone eats up 8 percent of the pie. For all its promise of opportunity and boasting about the middle class, the country looks uncomfortably like, say, Cameroon or Iran or Nigeria—all a bit more equal societies than the United States, by one measure at least.

That inequality and the Midas-type fortunes that go along with it necessarily raise many questions. But the one at hand is: What are the richest Americans doing with all that cash? In many cases, they are giving it away, and Slate is here to recognize them for doing so, as it has done for the past 15 years.

The Slate 60, compiled by the Chronicle of Philanthropy, encourages America's plutocrats to be as competitive about their giving as they are about their returns on investment or their summer homes or their yachts. (Read a history of the Slate 60 and an explanation of our methodology.)

For this year's Slate 60, total giving came to $3.36 billion—a princely sum, but nevertheless less than in years past, even the bust years of the recession. Indeed, the donors on the 60 granted $4.2 billion in 2009, $15.78 billion in 2008, and $7.79 billion in 2007. The drop in 2010 is mostly because there were no outlying, big blockbuster gifts or bequests, such as 2008's bequests of $5.2 billion by Leona Helmsley and $4.5 billion by James LeVoy Sorenson. The median gift—perhaps a better year-to-year measure—rose slightly to $39.6 million, though the median has also declined since the prerecession years. Though the totals came in lower than expected, still, 2010 proved a revolutionary year for giving—not in dollars and cents, but more importantly, in philanthropic culture. Over the course of the Slate 60's history, America's richest have gotten richer and richer and richer. But the calls for them to give it all away have gotten louder in turn. And this year, two of America's most important philanthropists threw away all propriety and seized the bullhorn.

In August, Bill Gates and Warren Buffett embarked on a very public campaign to convince the world's billionaires to donate their wealth. (Incidentally, though neither appears this year Gates, along with his wife Melinda, and Buffett are the top donors in the history of the Slate 60.) The campaign is called "The Giving Pledge," and it asks the super-rich to give away at least one-half of what they have earned, in their lifetimes or at their deaths. "I've worked in an economy that rewards someone who saves the lives of others on a battlefield with a medal, rewards a great teacher with thank-you notes from parents, but rewards those who can detect the mispricing of securities with sums reaching into the billions," Buffett wrote, reiterating his decision to give away 99 percent of his wealth. "That reality sets an obvious course for me and my family: Keep all we can conceivably need and distribute the rest to society, for its needs."

If tacitly—the project focuses on carrots, not sticks—the pledge called out America's richest for not doing enough for society. It caused a media maelstrom, both in the United States and abroad, and started serious conversations among the chattering classes. Forty American individuals and families immediately pledged to give up the bulk of their fortunes—virtually all of whom appear on this year's Slate 60 or on lists past.

Among them is Facebook founder Mark Zuckerberg, perhaps the most interesting figure on Buffett and Gates' list, and Slate's. He is just 26, meaning he has particularly strong incentives to hold on to his money, whether to invest back in Facebook, or to build a new company, or to lavish on his future children and grandchildren. But he, too, has promised to start giving it away. This year, he granted $100 million to an educational startup that will benefit schools in Newark, N.J., putting him in a tie for 10^th this year.

In other ways, though, the list closely resembles those of years past. Most donors come from the worlds of technology, industry, real estate, and, especially, finance, with relatively few coming from entertainment and sports. Investor George Soros, a perpetual figure on the list, came in first, granting a massive $332 million to his Open Society Foundations, which support a wide variety of justice, education, public health, and media initiatives. Behind him came Michael Bloomberg, founder of news and data giant Bloomberg, mayor of New York, and another permanent fixture. He granted about $280 million to 970 different charities and initiatives.

Also as in the previous iterations of the Slate 60, big givers overwhelmingly chose causes close to their homes or their hearts, often local organizations or their alma maters. And donations to health- and education-related organizations dominated overall giving again. This year's top donors gave to 21 different hospitals or health groups, and 33 different universities or other educational establishments. Arts, freedom, and religious groups rounded out the remainder. Foreign aid and assistance charities received relatively little of the pot.

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.