Here's a great option for those that want to protect the back of their shiny new iPhone 4, but also want to add a bit of flair. Gelaskins are a great option, easy to apply and easy to remove. And...
It also covers the antennas!
http://www.gelaskins.com/store/skins/phones/iPhone_4

It also covers the antennas!
http://www.gelaskins.com/store/skins/phones/iPhone_4