Check out the websites students are using in CAMP Computer:
http://www.typing.com (grades 3-5)
http://www.abcya.com (K-5)
Lots of educational links to challenge students!
http://www.starfall.com (K-2)
http://www.pbskids.org (K-2)
Lots of educational categories! (reading, rhyming, etc.)
http://www.scholastic.com (K-5)
http://www.turtlediary.com (K-5)