The app I mentioned last month, Motion Math is now available on iTunes, and has already been awarded the Children’s Technology Review's Editor’s Choice Award for Excellence in Design with 4.5 stars.
Here's how it works:
The game follows a star attempting to return to its home in a far-away galaxy by moving through different levels and uses tilt-action to progress. Learning fractions is the main aim of the game, and they're shown in different ways (decimals, pie charts, numerator-over-denominator, and percentages). The few reviews I've seen seem positive, lauding the creators for finding an engaging way to connect abstract ideas to concrete scenarios.