1. Robert W. Wilson Charitable Trust
ROBERT WILSON, 80
Robert Wilson Associates (hedge fund)
Latest year's giving: $52.5 million
Trust's assets: $166.9 million
Wilson wants to help preserve the natural world with huge gifts to the Nature Conservancy ($22 million), Wildlife Conservation Society ($13.6 million), and Environmental Defense ($6.6 million). (Read an interview with Wilson.)
Bonus fact: Gave $50 to Friends of Terra Cotta, a nonprofit focused on the preservation of—you guessed it—terra-cotta.

2. John Templeton Foundation
JOHN TEMPLETON, 96
Franklin Templeton Funds (mutual fund)
Giving: $44.3 million
Assets: $1.08 billion
His foundation is aimed at exploring the nexus of science and spirituality, thus gifts like the $3.6 million to the International Society for Science and Religion, which promotes dialogue between science and religion, and $2 million to the Spiritual Enterprise Institute, which focuses on the intersection of business and spirituality.
Bonus fact: The foundation awards a $1.6 million annual prize for contributions to planetary spiritual progress.

3. Simons Foundation
JIM SIMONS, 69
Renaissance Technologies (hedge fund)
Giving: $33 million
Assets: $477 million
A math-geek billionaire, Simons donates to both math and science causes as well as to autism research. The foundation gave $14 million to the State University of New York at Stony Brook, where Simons was once chairman of the math department.

4. Robertson Foundations
JULIAN ROBERTSON, 75
Tiger Management (hedge fund)
Giving: $32 million
Assets: $703.2 million
Robertson frequently focuses on education. His foundations recently donated $3 million to the New York City Center for Charter School Excellence.

5. Weill Family Foundation
SANDY WEILL, 74
Citigroup (commercial bank)
Giving: $26.4 million
Assets: $212.9 million
We all know Weill likes Carnegie Hall ($1.7 million), but he must love Cornell University ($24.6 million), his alma mater.
Bonus fact: Weill's foundation has been operating since 1967.

6. Mandel Foundations
STEVE MANDEL, 51
Lone Pine Capital (hedge fund)
Giving: $26 million
Assets: $147.2 million
Mandel gives a lot to education causes, usually in increments of $150,000 or less, but he ponies up big-time as well: Note an $18.5 million donation to the Fidelity Charitable Gift Fund.