After coming from a white senna case thats worn down after a year I just ordered a black leather iPhone case for my white iPhone4s from http://www.ikonicedge.com/
I've ordered a few different cases to try out w/ the White 4S. This SGP Vintage Brown was the only leather one. Doesn't offer much protection, but for $33 I'm giving it a shot.
I had the SGP Vintage for my iPad 1 and, it's a beautiful case, but got dirty way to fast. Guess I need to wash my hands more! haha
I have a white 4S and am using a green bumper right now but just ordered a Joli leather sleeve for mine (one of their re-designed cases). Brown with green interior. Can't wait for it to get here! www.jolioriginals.com
Good news is, iphone 4s has same shape as oreginal iPhone 4, this means iPhone 4 case exactly fit to iPhone 4s too.
If you are looking for genuine leather case for iphone 4s then i woud recommed HOCO iPhone 4 leather case or Miaget iPhone 4 Case, you can find them here