Now, new in the app store we have Pocket Magic, [App Store link] which presents a 'mind reading' effect you can spring on the unsuspecting.
The trick presents a colorful screen and asks you to select one of the many numbers that appear, and indicate what color it is. After some nice animation, you are asked to find your number again among the many on screen, and again indicate what color the number is again. At that point, the app can usually guess what number you selected. It also successfully predicts a magic color that appeared at the beginning of the trick. For many, this will be baffling, for others, not so much.
For assistance in learning the trick, there is an apprentice mode, which walks you through the simple steps to pulling the trick off, although most of the heavy lifting is done by the application.
One suggestion for the developers is that when choosing the numbers the ball selected should animate or glow so you are sure you made the right choice.
It's interesting how the iPhone seems to be a good platform for magic tricks, and many effects are coming out. It may be a good fit because there is something whimsical about the iPhone itself, coupled with the fact that one of the iPhone's strengths is that is really an entertainment device, as well as a cell phone, web browser and email mini computer.
I wouldn't be surprised to see increasingly sophisticated tricks appearing on the App Store shelves in the near future.