The following sites are helpful:
Math Websites:
www.aaa.math.com
www.factmonster.com
www.abcya.com
ELA:
www.abcya.com
www.scholastic.com
www.raz-kids.com
Science:
www.nationalgeographic.com
www.billnye.com
www.discoveryschool.com
Social Studies Online Textbook:
www.harcourtschool.com