Leander Kahney of Cult of Mac spotted this $0.99 app for the iPhone 3GS. It's called Car Finder and it helps you find your parked car.
The app uses the iPhone's camera to overlay the direction of your car and how far away it is. The app relies on the camera and a digital compass, and is compatible only with the iPhone 3GS running 3.1 or later.
Car Finder iPhone App Uses Augmented Reality To Find Your Wheels