Warren Buffett and Bill Gates were able to line up more than $100 billion in charity pledges from the American elite, but many of the richest in the U.S. haven't take the pledge to donate a majority of their assets to charity. Click here to see the billionaries who are also rich in the giving spirit.
NET WORTH: $12.7 billion Ahead of Perelman -- but still not cracking the list of the Richest 10 Americans -- Warren Buffett and Bill Gates had to reach down the Forbes list to No. 17 to land Paul Allen. (Philanthropic experts argue that casting a wide net and attracting pledges from eons of millionaires may ultimately raise more than targeting the select billionaire set.) With a fortune valued at over $11 billion, Allen is the second-richest technology executive on the Buffett/Gates list. He also shares a distinction with Larry Ellison -- that of being a college dropout.