I don't have an iPhone...I do have an iPod touch which is nearly the same. I don't have a case for it because I don't want some run-of-the-mill gel/silicone pink case. Those are boring. This, however- available in brass, aluminum, or titanium, is rather hella bad!
Exovault is a small artist-run company. The aluminum EXOvault case is lightweight and durable, and fits the iPhone 3G or 3GS like a glove. The EXOvault case is machined from solid metal stock in two pieces. Your iPhone will not rattle around or move within the case. And the case will not scratch your iPhone. Handmade in Brooklyn.