It seems there are several cases by Canon that will fit the S230, I have the skin tight leather one that only holds the camera, listed as the case for this particular model by Canon. This seems best for ultra portability. There is a larger one, more of a pouch that holds some extras like battery and CF cards. I bought this camera for its small size so I wanted the smallest case, the accessories I would normally carry with this camera can go in my pocket.
The metal case has the cool factor, hard to find, never sold in this country officially. If you want a tight seal, look at the Pelican 1010 micro case, plastic but quite a bit bigger than the metal Ixus case: