There is much material, well organized in the site. Teachers can access problems, research and links to updated materials from, for example, the National Council of Teachers of Mathematics. One interesting site is the Mathematics Quilt which features pictures of mathematicians both male and female. When users click on the picture, they can get information about how that person uses mathematics in his or her job, and some stories about their study of mathematics. It could be inspirational to students.
This material can be used to address a variety of topics in math including teaching and learning of basics skills, as well as more advanced concepts such as math beyond school.