Math 
Convergence Currently available at no charge, this online mathematics journal published by the Mathematical Association of America aspires to teach math principles through history. The site is searchable; registration is required.
The Data and Story Library The DASL was funded by a grant from the National Science Foundation to create an archive of abstracts and datasets related to statistical concepts.
Fibonacci Numbers and the Golden Section This site is hosted by the Department of Mathematics, Surrey University, UK. It serves as a gateway to sites on Fibonacci himself, an introduction to Fibonacci numbers, and applications of Fibonacci numbers and Golden sections in nature and the arts.
MacTutor Produced by the University of St. Andrews in Scotland, this site contains links to the biographies of over 1300 mathematicians, over 30 articles on the history of mathematics, and the history and description of "famous" curves.
Math and Science Gateway Cornell University hosts this website, which links to resources appropriate for high-school students and educators.
Mathwords Created by a math teacher, Mathwords is an interactive math dictionary of terms and formulas from introductory algebra to calculus.
Mathworld Author Eric Weisstein created and maintains this detailed, constantly updated mathematical encyclopedia.
The Prime Pages This award-winning site contains a wide range of resources on prime numbers, including up-to-date discoveries of the largest prime, a list of primes, a history of primes, and mathematical theories related to primes.