My homeschooling co-op recently had a discussion about educational video games for kids. Here is a summary of my contributions to that discussion.
World of Goo
This game helps kids with physics. It doesn't teach them F=ma, but it helps kids develop their intuitive knowledge. It's a puzzle game, and the goal is to build large structures with balls of goo. You can buy and download this game at WorldOfGoo.com
The kids take an organism when it's just microscopic and guide its evolutionary process to becoming a complex animal, forming civilizations, and going to space. My kids have learned a bit about genetics, trade offs between fighting and forming friendships, and much more. My children love this game. Again, like World of Goo, the knowledge they learn is not specific equations, but they develop an unconscious understanding. Spore can be purchased and downloaded at spore.com.
Ikariam is a free, web-based game. I think this game is particularly applicable when studying topics such as ancient Greek city-states, or any small group of people growing and expanding. You start off with 40 people and a little bit of wood. Players build a town hall for people to live in, research scientific fields so they can do new things, determine how many of their people should work in the lumber or elsewhere, and build defensive walls and other buildings in the town. Players must balance economics and the happiness of their people while protecting the town from other players that might attack them. Players can form or join alliances and learn how to plan strategic battles. My husband and I both played this game for a while. (My husband still does.) My 7-year-old son also plays this game. I'm convinced that dealing with the trade-offs in Ikariam helps him understand how there are trade offs in all aspects of life. Go to ikariam.org to play this game.
My daughter knows how to type, really type, not just hunt and peck. My son is learning. I didn't teach them. I had my daughter play Dance Mat for about ten to fifteen minutes a day, and after a few months, she could type. I didn't force her to play either. I just told her to do her typing and she jumped at it with alacrity. This is a free, online game published on the BBC's website. Animated animals explain how to type, including proper fingering, home keys, and the like. Four different levels present different challenges and different games for the kids to play whilst learning.