I have been having too much fun playing games at History.com. The State that Plate Game is HARD.
And if you want a better Place the State game check out Addicting Games for one that gives you how many miles off you are.
Sheppard Software has awesome games; everything from the food chain to vocabulary.
If you are more into reading games you might like Kabongo. I am not sure my kids actually got to the games section, they were having too much fun designing their character.
Don't leave the preschoolers out, theres stuff for them too so they can feel like a big kid.