Enchanted Learning

abcteach

OSLIS (elementary)

OSLIS (middle and high school)

Starfall

FunBrain

Math Flash Cards (Math Activities)

Gamequarium

The Internet Public Library Kidspace

Fact Monster

Kid Info

Math.com

National Geographic Kids

B.J. PinchBeck's Homework Helper

Science Fun for Your Kids

from NAESP (National Association of Elementary Principals)