A colorful dictionary of math terms for students. The site includes nice visual and math examples of the terms.
The website for James Stewart's collection of Calculus texts. Stewart's texts are widely used in Calculus courses. The site contains a lot of supplementary material, including review material (e.g. -- need a quick brush-up on algebra concepts? check out the algebra review).
Glencoe is a major textbook publisher, and Dvorak Tech Academy uses their literature books for grades 6-8 basal readers. This is the companion website, where teachers may find resources to support the text-based lessons.
A math glossary. The list of terms varies according to the selected grade level.
The Math Open Reference Project is in the process of creating a free online interactive math textbook. At last look the emphasis was on geometry. The site includes printable classroom materials.