Apple is trying to be all futuristic with its use of stainless steel and oleophobic glass, but perhaps you’re more inclined to look a little more natural. If that’s the case, you might want to check out the new wood skins from Karvt.
Karvt’s website says the skins are made of “100% real wood, which is both sustainable and eco-friendly.” I don’t know how cutting down trees for iPhone skins is “eco-friendly” but I guess it works for marketing purposes. This is a step above those plastic screen protectors, and they use professional grade 3M backing adhesive that sticks perfectly. It won’t do you any good against the death grip phenomenon, though, since they only attach to the front and the back of the iPhone; the metal outer ring remains untouched. If you did drop your iPhone 4 and the glass shattered, this would keep it in place and hidden from sight.
For those of you who feel inclined to give your iPhone a woodie, so to speak, you can take your pick from chocolate walnut, natural cherry, pine, maple, and bamboo (which is probably the only eco-friendly version, since bamboo grows like crazy). They sell for a cool $25.