National Geographic for Kids http://www.nationalgeographic.com/kids/
Scholastic Books You may order books online, from flyers your child brings home from school. They are reasonably priced. Our class receives free books according to points 'earned' by our orders.
'An amusement park of math designed for fun' http://www.coolmath.com
Click on math for games and challenges. http://www.framingham.k12.ma.us/dunning/kidspage.htm#math
U.S.Dept. of Education Helping your child learn mathematics. Free online book, 'Helping Your Child Learn Mathematics'... activities suitable for children in preschool through 5th grade.
Visualizing huge numbers in pennies. For kids 5 - 95 !