Continuing one of its least impressive leather case lines, Vaja has released iVolution Grip ($30), essentially two pieces of high-quality leather that have been wrapped around an overly simple hard shell; it covers only the sides and back of the fourth-generation iPod nano. What's new in this year's Grip is the option to add Rivet metal clips, such as the $14 GoClip here; the spring-loaded, ball joint-mounted clip is far more interesting than the…
