Here is a partial list of my favorite websites that I often recommend to my mathematics students.
Click here for Curriculum Resources: http://www.holliston.k12.ma.us/adams/curriculumresources.htm
Math Puzzles that are fun! http://www.cut-the-knot.com/games.html
Math for Morons Like Us! (That REALLY is the name) http://library.thinkquest.org/20991/intro.html
My favorite site ever for Math! Very comprehensive and easy to use. http://www.aaamath.com/grade8.html
Here is an easy math dictionary! http://www.harcourtschool.com/glossary/math2/index6.html
A site for real life application of mathematics. http://www.learner.org/exhibits/dailymath/
Great site for Pre-Algebra vacation project: http://www.expedia.com
Another site for Pre-Algebra vacation project: http://www.hotels.com
Helpful website for worksheets and extra practice: http://math.com
National Library for Virtual Manipulatives in Math. A big hit with everyone! http://matti.usu.edu/nlvm/nav/index.html