Digital Lifestyle Outfitters (DLO) today unveiled its newest line of nano shell cases, specifically designed for the second-generation iPod nano. Offered in five nano-matching colors, each DLO Shell for nano comes equipped with two interchangeable backs — a smooth, transparent back and a reinforced, opaque back with a built-in belt clip.  Both offer a superslim, form-fitting case for the iPod nano. The polycarbonate cases retail for US$19.99 and are available now.