White House for Kids http://www.whitehouse.gov/kids/whlife/index.html
National Geographic for Kids http://www.nationalgeographic.com/kids/
Fun activities - by girls....for girls. http://www.missoandfriends.com/
Reading for kids http://www.starfall.com
MathCats-- Emphasizes the logic and beauty of math, rather than drills and practice. Provides open-ended and playful explorations of important math concepts through on-line games, off-line crafts and interactive projects. Requires a free MicroWorlds download. Warning: it contains TETRIS! http://www.mathcats.com