Math-Net
Providing results of mathematical research and development, teaching material, and information about working mathematicians and mathematical institutions.
www.math-net.de

Math for America
Group of mathematicians, business people, and educators with a mission to improve math education in America's public schools.
www.mathforamerica.org

Foundations of Computational Mathematics
A nonprofit organization that supports and promotes research on fundamentals of computational mathematics.
www.damtp.cam.ac.uk/user/na/FoCM