I have the Seidio Innocase 2 on mine and it's extremely nice. I have quite a few friends with iphone, all having various cases on theirs and they ALWAYS say 'wow, that case is better than mine, what is it? I'm getting one'. I'm actually surprised the reviews for this thing aren't higher.
First off, it's a "full protection" case in that it comes up very slightly above the front face so even if you set it down on the face, its protected. Its incredibly thin, less than 1mm (I think their site claims 0.8mm), yet is a hard plastic shell with a very nice rubberized soft touch coating, the best I've seen from any case. it's also felt lined on the inside so it'll never scratch your phone. The fit and finish are superb.
I have yet to find another case that offers this much protection in a thinner package. If anyone knows of one, please let us know about it! Check out the innocase 2, it's very nice.