I tried a plastic cover on the front and back that I really had good results with on my old iPad 2. The brand is Ghost Armor and it seemed clearer to me than Zagg. However, on the new iPad with the Retina display it just was not invisible. Looking very, very closely would reveal small less-than-pixel sized problems -- enough that I finally stripped off the front screen and am just going with the back. My feeling is that the retina display is sooooo perfect that you do not want to fool with it, just be sure to keep your smartcover closed. And, yeah, I would cover the back so as not to mar that area and also it protects the side of the case from tiny scratches sometimes caused by the smartcover attaching there. Next, I picked up at a Fossil store an iPad carrier that is sort of distressed leather and fabric in muted earthtones -- very cool looking. I bought it for the iPad 2 and it fits the new iPad fine (with smartcover attached). I think the stores still have them and they are a great buy at around $30 or so.
I had the Oberon on my Kindle and bought one for my iPad 2 -- they are simply the most beautifully designed and made cases out there. On the other hand I took it off my iPad 2 and will not get one for my iPad (new). That is because of the weight and the tickness. I use my iPad for ereading. Folding back that thick leather case makes the feel of the iPad a little unwieldy and it does add a great deal of weight. But if you can get by that the Oberons are just top-notch as far as looks.