These two new silicone rubber case designs for the fourth-generation iPod nano may share the same name, but they're pretty different in terms of features and physical design. The basic Sport Grip ($15) features stylish dotted sides for extra grip, and comes in three colors -- white, black, and clear -- each with included protective film and a cleaning cloth. By comparison, Sport Grip Deluxe ($25) adds a soft lanyard necklace and a circular hook to…
