If you're looking for a good magic trick to show off your iOS device, give Magic Trick #1 a try (US$0.99).
When you perform the trick, the spectator sees several cards. He or she names either the pip or picture cards, the type of card and the suit. You as the performer pick up your iPhone or iPad, which shows a black screen. You then rub the screen, scraping away the black and revealing the chosen card.
The magicians out there will have some ideas of how the trick works, but I have to say there are some subtleties that flow so smoothly from your actions that I don't think most people will catch them.
The app lets you watch a tutorial before attempting the trick. In my demonstrations, the trick fooled four people who couldn't guess how it was done. You can repeat the trick and you can show a different card, but repeating too often will give the trick away.
Magic Trick #1 is a universal app, and it requires iOS 5.1.1 or greater. It is optimized for the iPhone 5.