6. Larry Ellison (CEO, and Founder of Oracle)

Estimated worth: $36 billion

Estimated donations: $808 million 

Charity: Ellison Medical Foundation 

Though he was blamed for insider trading for selling $1 billion of his company's stock in 2001, Ellison redeemed his image by donating one percent (over $150 million) of his fortune in 2005 to charity.

In response to the September 11th terrorist attacks, Ellison made a controversial offer to donate to the Federal government software that would enable it to build and run a national identification database and issue ID cards.

In August 2010, Ellison became one of the 40 billionaires who signed "The Giving Pledge”. Ellison wrote: "Many years ago, I put virtually all of my assets into a trust with the intent of giving away at least 95 percent of my wealth to charitable causes. I have already given hundreds of millions of dollars to medical research and education, and I will give billions more over time. Until now, I have done this giving quietly—because I have long believed that charitable giving is a personal and private matter."