lots out there . . . unfortunately and I know I am going to get slammed for this but really neat developments in Edutainment stopped in the late 90s. Games like KidPix, MathMunchers, WordMunchers gave way to "LeapFrog" and "Nanosaur" - insipid, craftless, uninspired, inorganic logic and gorgeous fluff... Games like MathMunchers could take a kid from basic math to calculus - of course what teen or premature genius wants to play a game where mutant QBerts chase you around to solve problems? Well you might work real fast to make sure the little f@#$ don't ever show up on screen
okay I'm finished - oldies but goodies reside at:
http://mac.the-underdogs.org/
a personal fav - when my kids were young was JumpZampoli (OS9 again but when you really don't want the kid to learn what the "BFG" is -) this game is fantastic, teeter-tot balloon popping.
I can actually highly recommend the following for the 7 to 15 year old - they love power structure games and these will take on their own life as kids get smarter and greedier...

SimCity 2000
RailRoad Tycoon 2 Gold [RRT3 is great too but we always love cheap]
There was also a dinosaur photography game for a little while where you had to run around and take pictures and ID dinosaurs but I think an online auction is the only place to find that one. good luck and remember what interests you will hold the interest of the kid.