Some thoughts about educational games for the iPad

One of the reasons I treated myself to an iPad last year was that I saw great potential for educational (and fun) games for kids. I was hoping we could further delay getting a Wii or DS or other console, and nudge the kids into some educational games to boot.
I have been pleased so far, but of course the games are mixed. I thought I would share some thoughts about different kinds (and qualities) of educational games, using a few examples as case studies.

My favorite pair of educational games for the iPad is the Stack the States (and Countries) games.
The game works like this: You answer trivia questions about the states, when you get an answer right, you get to stack the states. Once you reach a certain line, you are awarded a state on your map. The gameplay is a simple physics/puzzle game, where you have to figure out how the shapes fit together, and balance them to reach the line.
Why am I a fan? First, it is pretty fun. The physics-based puzzle gameplay is challenging in a simple video game way.
The second reason that I like it is that it does a good job mapping the relevant dimensions of gameplay map onto  good educational dimensions. What the heck does that mean? Instead of just being a glorified trivia game, where you get points for answering questions right, the stacking task integrates relevant state facts into the game itself. In this specific case, you naturally learn the shapes and sizes of the states as you do the stacking. I bet a few hours of playing this game, and kids could do a pretty good job sorting states from smallest to biggest, without even trying to memorize this.
For improvement, I would love a difficulty setting for the trivia questions, which are fairly limited right now. But for a 3.00 purchase, I have gotten more than my money's worth. I highly recommend it.

Another game, which don't like as much, but still ok, (and is typical educational software fare) is called Math Ninja.
This is a very simple arcade shoot-em up, where you answer math questions (addition, subtraction, multiplication, division) in between rounds of shooting evil robot cats and dogs. This game follows the model of bribing kids to do math drills by interpersing them with a video game. I am not totally against this approach (and this game is a pretty good execution, you don't just get points, but you unlock weapons by answering more questions quickly). Sometimes you just need to practice, and drill, and math facts are a likely candidate. I am ok with bribing my kids to memorize the times tables just so long as that doesn't become how they think of all math.

Anyways, those are a few quick thoughts. Any other iPad educational game recommendations out there? The boys have discovered the periodic table of elements, thanks to They Might Be Giants. I wonder if there is a game to be made from that?