Math
Pure Mathematics

• American Mathematical Society
• Conjectures in Geometry -- "a wide variety of activities (demonstrations and assignments) utilizing computer software that could be incorporated into a high school geometry classroom."
• Constants and Equations-- for scientific use
• Dave's Math Tables-- basic identities, polynomials, hyperbolics, volumes and areas, vectors, integrals, Fourier series, with diagrams included.
• Famous Problems in the History of Mathematics--from the Math Forum at Swarthmore, with detailed discussions of each, as well as an annotated list of books on the history of mathematics, and a useful set of links.
• Geometry Center
• Geometry in Action -- "This page collects various areas in which ideas from discrete and computational geometry (meaning mainly low-dimensional Euclidean geometry) meet some real world applications. It contains brief descriptions of those applications and the geometric questions arising from them, as well as pointers to web pages on the applications themselves and on their geometric connections. This is largely organized by application but some major general techniques are also listed as topics"
• History of Math Archives-- Includes biographical information on thousands of mathematicians, searchable by name or time period.  Also includes other numerical systems throughout the world.
• Interactive Geometry--a Guide through Euclid's Elements
• the Pi Pages -- needs JAVA
• a Short Course in Trigonometry--by Prof. David Joyce at Clark University.
• Trigonometric Functions and Calculus--for liberal arts and business majors.