Project Mathematics! is a collection of videos that explore basic topics in high school mathematics.
Algebra Project is a 501 (c) (3) national, nonprofit organization that uses mathematics as an organizing tool to ensure quality public school education for every child in America. The algebra project includes an interactive curriculum designed to help inner-city and rural students better understand mathematical concepts. Developed by Bob Moses, a mathematician and civil rights leader, the curriculum calls for students to follow a five-step process in which they use their physical surroundings as tangible references for mathematical ideas. With the help of an NSF grant, the algebra project is being introduced to Los Angeles under the aegis of One-LA.
Also check out Others and General for other resources including computer games for developing intuition about topology and geometry, virtual math communities and on-line question and answer services for students and teachers.