Augmented reality concepts excite us. We love overlaying stuff on a video feed of the world around - it lets us feel like we're living in the future.
The latest application of the iPhone 3GS' video camera lets you overlay the nearest tube stops for every line on your video camera. To accomplish that, it uses the GPS, compass, and camera.
Holding it flat, the app shows an arrow pointing in the right direction, and holding it upward means that you can see more info - distance, relevant tube lines and other stacked stops behind the one you're looking at.
The app has been submitted by makers Acrossair for inclusion in the app store, but isn't there yet. Also, it'll only work on the 3GS, and is only really of use if you live or work in central London. Still, there's no reason why it couldn't be modded for other landmarks. More of this sort of thing please, developers.