Apple's iPhone 4 is a beautiful phone, but that glass back sure makes me nervous when I'm pulling it out of my pocket. Sure, I could get a case to help protect the fragile design, but do you really want to uglify such a pretty phone up with a bulky case?
Here's a nice solution: just replace that glass altogether. For a mere $13 you can get a brushed metal back that you can install by just popping out a couple of screws. It's designed with the same markings on the back and everything, so you'll be sure to trick all sorts of people into thinking you've somehow acquired the iPhone 5.