Math

OpenCurriculum has released a free 5,000-document library on its website for math teachers to use as lesson materials. Anyone can use the material on the website without logging in, but to get access to tools such as the lesson plan builder, you need to create an account. The tools aren't tailored to a particular subject:

Interactivate is a set of free, online courseware for exploration in science and mathematics. It is comprised of activities, lessons, and discussions. The site is structured around collections of activities, lessons, and discussions. You can reach listings of each type of resource either by following the prominent links (2)(3)(4) on the front page, or by using the "Jump To:" pull-down menu (1) located at the top of every page:

Figure This!  Math challenges from the National Council of Teachers of Mathematics:

NRICH: Mathematics enrichment for all grade levels: