(5) Marie Curie
Science's undisputed first lady has a C.V. that may never come along again. Along with her husband Pierre, she discovered the chemical elements polonium and radium. The tag team also discovered radioactivity, which netted her the 1903 Nobel Prize for Physics. Even after Pierre's death in 1906, Marie kept working and eventually isolated pure radium, which won her the Nobel Prize for Chemistry in 1911. Her name is still synonymous with radioactivity, a word she coined. Even more impressive: she did it all as a working mother.
(12) Linus Pauling
No scientific slouch himself, Pauling won the 1954 Nobel Prize for Chemistry for his work on the nature of chemical bonds and the structure of molecules. Pauling then turned his attention to humanitarian efforts, specifically an attempt to ban atmospheric nuclear weapons tests. He collected thousands of scientists' signatures on a petition to warn the United Nations of the dangers of nuclear testing and proliferation. His pacifist politics got him in hot water with Congress, but they also netted him a second Nobel, the 1962 Nobel Prize for Peace, which he accepted on the day the Nuclear Test Ban Treaty went into effect.
The competition in the two-Nobel division is pretty fierce. Curie's the only person to win Nobels in two different scientific disciplines, but Pauling is the only person to ever win two unshared prizes. Then again, Curie gave birth to another Nobel winner; her daughter Irene won the chemistry prize in 1935. Pauling may have saved us all from a nuclear holocaust, though. There are no wrong answers here.
[See the whole bracket here.]