I just took a look at my DD13's apps, here are a few;
Oregon Settler, Tiny Zoo, Alchemy, Magic Piano, Cat Jokes, Warrior Cats, Go Sky Watch, Google Earth, NASA, Solar Walk, Skype, Pandora and many more......
ETA: The educational apps we have are really geared to younger kids, but DD13 does play Stack the States, Presidents vs Aliens, Stack the Countries (this one is hard! Lol) Math Ninja and Monster Physics.
There is an app called Apps Gone Free which is fabulous! We've gotten many very cool free apps that way.