Math Investigations http://www.pearsonsuccessnet.com
(Sample link) National Geographic for Kids http://www.nationalgeographic.com/kids/
(Sample link) Fun activities - by girls....for girls. http://www.missoandfriends.com/
Playhouse Disney http://www.playhousedisney.com
PBS http://www.pbskids.org
Starfall http://www.starfall.com