Here you have a list of 400 American Mathematicians
http://en.wikipedia.org/wiki/Category:American_mathematicians
Here there are some I know ( I get pardon, as my culture is so limited ), from science books:
Norbert Wiener (November 26, 1894, Columbia, Missouri – March 18, 1964, Stockholm Sweden) was an
American theoretical and applied mathematician. He was a pioneer in the study of stochastic and noise processes, contributing work relevant to electronic engineering, electronic communication, and control systems. Wiener is also the founder of cybernetics, a field that formalizes the notion of feedback and has implications for engineering, systems control, computer science, biology, philosophy, and the organization of society.
George Bernard Dantzig (8 November 1914 – 13 May 2005) was an
American mathematician who introduced the simplex algorithm and is considered the "father of linear programming". He was the recipient of many honors, including the National Medal of Science in 1975, and the John von Neumann Theory Prize in 1974.