KMC S-10 is what i'm using. It's 1/8", made for single speed / fixed / IGH applications, just as the gates drive is. I'm not aware of any purely stainless multi speed chains, Wippermann has a few chains that are multi speed with stainless inner links though.

One other thing that has bothered me about the Gates system is that on their faq they only loosely state that it "lasts twice as long as a regular chain", but they don't specify what chain they're comparing it to, what the comparative drive train setup, and what the true expected lifespan is. As a result, their claim is pretty vague. Regular chains have widely varying lifespans. A single speed or IGH setup with a good 1/8" chain already outlasts a normal derailleur based thinner chain setup by quite a factor on its own. I'd like to know what gates is really basing their claims on. I don't doubt that their belts can last quite a long time, but it'd be nice to know more precisely what they're going to give relative to the other options, because some of the other options last months, while others last years.