I've never heard of a deal like this, but we'll take it anyway. Halfbrick's great game Jetpack Joyride (one of the best iOS games of the year, honestly), is being given away for free by none other than Apple. You have to be a Facebook member, but if you 'like' Apple's official App Store Facebook page, you can get a code that will nab you a free copy of the game from the App Store.
The one catch is that you have to essentially allow Apple access to your information on Facebook, but all it's asking for is to have that information (which might be public on your profile anyway, depending on your settings). It's worth nothing that the company doesn't ask for the right to post things on your profile, though those concerned about that probably won't take the deal anyway.
At any rate, as long as you're OK with seeing your name attached to Apple on Facebook (and this is an official Apple account), you can get a free Jetpack Joyride code! Enjoy.