Every iPhone I have ever owned going back to the original has been protected with the invisibleSHIELD line of protective coatings from ZAGG. The stuff is very tough and transparent and you can hardly see that it is on the device when installed.
The coating originated in the military and was used to protect the leading edges of helicopter rotors to make them last longer. Zagg has announced that the scratch prevention film is now available pre-cut specifically to fit the new MacBook Air notebook computers.
The film is easy to install and is available to fit the 11-inch and 13-inch models. The full body coverage for the 11-inch notebook is $54.99 (USD) and you can order a set of the films right now.