NASA for high school students http://www.nasa.gov/audience/forstudents/9-12/features/index.html
National Geographic http://www.nationalgeographic.com
Visual Fractions - at interactive review of fractions http://www.visualfractions.com
Math Forum - Site has a wealth of information on all grade levels of math http://mathforum.org/students
Mathsis Fun - Lots of information and math help http://mathsisfun.com/geometry/transformations.html
Mister Teacher - Animated examples of math information http://misterteacher.com/abc.html