Ask Dr. Math
A great math site on the Math Forum. Check out their
homepage, too - it's loaded.
Mathworld
A stupendous site from the makers of Mathematica.
History of Mathematics
Also includes biographies and career profiles of many
mathematicians.
MacTutor History of Mathematics
The name says it all.
Biographies of Women Mathematicians
Because after all, Archimedes would be nothing without his
wife.
A Selective History of Science on
Stamps
Includes many math and science stamps.
College Board AP Central
Learn about AP courses for next year here.