Math Dictionary for Kids http://www.amathsdictionaryforkids.com/
Math Surf http://www.mathsurf.com/
Investigations Math http://investigations.scottforesman.com/
Weekly Brain Teasers http://www.eduplace.com/math/brain/index.html
Fact Practice designed by 4th graders http://library.thinkquest.org/3797/bppracticefacts.html
Interactive Math Dictionary for Kids http://www.teachers.ash.org.au/jeather/maths/dictionary2.swf