National Council of Teachers of Mathematics
Nctm: Standards for School Mathematics
This standards-based NCTM website offers resources for teachers of mathematics for all grade levels, including interactive math tools, lesson plans, online resources, and the like.
University of Vienna (Austria)
University of Vienna: Maths Online
The University of Vienna, Austria, created this site to help bring the worlds of math and technology together. You have access to many applets and downloads that allow you to create lessons, tests, and puzzles. There are also great...