GeoGebra

GeoGebra is a dynamic mathematics software for schools that joins geometry, algebra and calculus. And, its free! GeoGebra is an interactive geometry system. You can do constructions with points, vectors, segments, lines, conic sections as well as functions and change them dynamically afterwards. Equations and coordinates can be entered directly. Thus, GeoGebra has the ability to deal with variables for numbers, vectors and points, finds derivatives and integrals of functions.
Sound far out; we think it worth taking a look.

AAA Math

Aside from the advertising, which is really pretty light, I really like this site. AAA Math features a comprehensive set of interactive arithmetic lessons. Unlimited practice is available on each topic which allows thorough mastery of the concepts. A wide range of lessons enables learning or review to occur at each individual's current level. Immediate feedback (simply the right answer)prevents practicing and learning incorrect methods, which is a common result of traditional homework and worksheets. Practice can continue as long as desired in a non-threatening format which helps build self-esteem and confidence. This is a really good tool for building a solid math foundation.

Kindergarten thru 8th Grade