We think we found currently the best one dedicated to iPhone 3G:
This is the SwitchEasy CapsuleRebel. It is composed of a soft adaptive polymer covering the iPhone case, then an over-all hard shell exo-skeleton frame made of polycarbonate further protect the device from impact. (on the back and sides).
We did not want to carry a crash test; however, this is most likely the most complete protection currently available while still featuring a belt clip. Of course, as the Apple logo is not visible anymore you will not be able to use it to show off.
