http://www.starfall.com/
A wonderful site for younger children to learn to read and learn their abc's.

funschool.com
This site is fun for all ages.

Funbrain.com
To be challenged for math problems, check this site out.

http://www.enchantedlearning.com/Home.htm

This is a great site for children to find exciting things about dinosaurs, ocean, etc.

http://pbskids.org/
A site for younger children

http://www.scholastic.com/kids/
Briefly summarize why the information on the site to which you're linking is useful.