The 5 is a little longer and lighter, has a larger display and better resolution. Better processing power, A5 vs A4 chip, as mentioned before works on 4GLT networks, camera pretty much the same; other than Video capabilities are better and you can take Still Photos in video mode.. some other slight differences, but not that much. The main thing really, you cannot buy a 4S with more than 16GB through a provider anymore, so to get more you have to buy the 5. Here's a side by side comparison of the 3 models currently available:http://www.apple.com/iphone/compare-iphones/
If you have the iPhone 5 you can go to Google Earth and instead of just showing you pictures it will actually take you there. At least that's what I heard on the Internet. You have to be careful though. If you go to a place where there's no cell towers you might have a hard time getting back.