#5 John and Laura ArnoldAmount donated in 2013: $296.2 million
Net worth: $2.8 billion
Beneficiary: Laura and John Arnold Foundation in Houston, Tex., and Fidelity Charitable Gift Fund in Boston, Mass.
Background: John Arnold founded hedge fund Centaurus Energy, and Laura Arnold is a former corporate lawyer. Their philanthropy program supports improving the reliability of scientific research, K-12 public education, the criminal-justice system, and public-policy practices.