The new iLumina case from BodyDock give you swappable bands and back covers. The basic shell case can be customized in many different ways. The case also had an added benefit once purchased. BodyDock will send you a free colored band and back panel once a month for six months.
BodyDock is a pretty cool magnetized system that allows you to attach your phone to a variety of different locations. Basically anywhere you can fit a small magnet, you can clip on you iPhone. This is a pretty unique idea ...