While I love the new Smart Covers for iPad 2, the one thing that they don't cover or offer any protection for is the back of your iPad 2. I wanted to protect my iPad 2's back from scratches. Since I was already a fan of Gelaskins, I ordered one on day one for the iPad 2. However, there are some out there that don't want to commit to a design or photo. Jim Nichols turned me on to the Zagg InvisibleSHIELD. While the picture above looks like a naked iPad on the left, it's actually sporting an InvisibleSHIELD. Both of these products are Smart Cover compatible and offer scratch proection for the back. Now keep in mind that the corners are still exposed and they offer no protection whatsoever for a drop or hard bump. If that's the kind of protection you need then you're better off getting a case. However, I love the thinness of the iPad 2 with Smart Cover and for my iPads I'll be sticking with skins.
You can see the Gelaskin skins here (for more than just iPad).
You can see the Zagg InvisibleSHIELDs here (for more than just iPad).