Couldn't find a list on their site, but they do have many countries across the world included. As for North America, here's the list (taken directly off the Satski app on my iPhone):
Aspen - Buttermilk, Highlands, Aspen Mountain, Snowmass
Obviously many are missed, but that's their version of "large" resorts. If your mountain is on the list, it's well worth the small cost. I think Satski is very good. Mine are not on the list, but I bought it anyways in the hopes they would be (or added later). Alas, that's not the case. So I settled on Ski Tracks instead. Doesn't link to resorts, but it has most other features I want.
Hope that helps!
BTW, on the iphone, the App is officially called Satski 2.0. For some reason it shows up as "lite" but it is indeed the full (paid) version.