kids.nationalgeographic.com teaches kids about how our world works and how having that knowledge helps them to be successful citizens in it.
http://kids.nationalgeographic.com/
http://kids.nationalgeographic.com/
starfall.com is a website that offers a bit of math, and a lot of reading and phonics exercises.
http://www.starfall.com/
http://www.starfall.com/
switchzoo.com is a really fun and engaging way to learn about many different kinds of animals and their habitats.
http://www.switchzoo.com/
http://www.switchzoo.com/