Dana Randall (my PhD advisor)
Alistair Sinclair (my advisor's advisor)
Mark Jerrum (my advisor's advisor's advisor)
Leslie Valiant (my advisor's advisor's advisor's advisor)
Mike Paterson (my advisor's advisor's advisor's advisor's advisor)
Tom Morley (one of the excellent professors at Georgia Tech)
Front end for the Los Alamos Science ArXiv
Eric Weisstein's World of Mathematics
Wolfram Alpha Mathematics page
Mathematician of the Day
Interactive Mathematics Miscellany and Puzzles (cut-the-knot.org) A veritable plethora Java applets illustrating many mathematical problems, apparent paradoxes, etc.
POP Mathematics Archive A collection of miscellaneous mathematical information.
Women Mathematicians A source for biographies, information, and other resources about women in the field of mathematics).
Why is there no Nobel Prize in mathematics? Speculation and opinions (both fact and fiction) can be found at this sight.
Win a million dollars (and have your name live forever). Solve one of the seven millennium mathematics problems and get a million dollars from the Clay Institute.