i used skinomi for a while on my Pre and my wifes pixi. love it = and excellent customer service. i just put it on my nexus but this time i tried the carbon fiber back - but i like the regular clear skin better on the back.
I ordered a skin from Phantomskinz from their Chromatics line. Waiting for it to show up in the mail. I think was originally made for the TMobile version of the phone, so I don't know that it's going to fit the Sprint version. The skins are well reviewed, but I guess I'll have to wait and find out about the fit.
Can you take a picture the back of your phone? I am curious to see how well it covers the Nexus 4G "butt."