I have a Samsonite case (a simple belt clip one, but rather strong) that I have left over from my X10.
I'm not sure if the demensions are okay for the Xperia S, as (yes i know its a bit dumb) I am not sure the exact dimensions the phone :/
anyways, I have something similar to the one linked below:
I will update this tomorrow when I get my phone in. I fear it may also be a little snug lengthwise :/
Got the phone, but it won't fit :/ so my search continues for the perfect case.