http://funschool.kaboose.com/: A fun website that introduces all core subject areas. There are fun arcade games for kids to enjoy.
http://www.funbrain.com/: A website that focuses mostly on language arts and math skills. It also has fun arcade games for kids to play.
http://mathplayground.com/: A website that focuses on math skills.
http://kids.nationalgeographic.com/kids/: A website where you can watch videos, look at pictures, play activities, and learn about your favorite animals.
http://pbskids.org/video/: Some great children's programs and video clips. Show such as Author, Dr. Seuss's Cat in the Hat, and many other children's programs are on this site. You are also able to play interactive games at this site.
http://www.rochesterpubliclibrary.org/kids/index.html: Here kids can play interactive games and puzzles that go along with stories that can be read to them on this site. My biggest recommendation are the tumble books!
http://www.mhschool.com/math/2009/ca/assets/factdash.html
http://www.sheppardsoftware.com/web_games.htm
http://kids.nationalgeographic.com/Games/GeographyGames/Geospy
http://www.mathplayground.com/balloon_invaders.html
http://www.arcademicskillbuilders.com/
http://www.yourchildlearns.com/mappuzzle/us-puzzle.html