HippoCampus is an educational site for secondary teachers. "Teaching with the power of Digital Media" is their slogan and I am very impressed with the layout and content. This is not just a site filled with games, but rather with lesson planning tools and educational content.
Use materials found here for display during guided instruction or on a computer station for tutorials. Students can work in a group or independently and the activities are self-checking and self-pacing.
Content includes: Algebra, Geometry, Government, Biology, Calculus, Environmental Science, Physics, Psychology, Religion, Statistics, and US History. (The Algebra and Calculus sections are also presented in Spanish!)