New to Griffin's iPhone 4 case lineup is Motif ($20), an inexpensive TPU plastic case that follows in the generally positive history of competitors' hydrocarbon iPhone 3G/3GS designs. Motif features a glossy smoke-colored soft plastic body that provides top and side button protection, plus highly contoured holes for the headphone port, microphones, rear camera, bottom speaker, Dock Connector port, and ringer switch -- tight around the headphone…