Apart from the well known japanese whetstones (which come at quite a price), there are many other natural stones all over the world, that can be used as sharpening stones.
Who ist using whetstones other than japanese? And why? I am looking for a really obscure stone (although the most obscure is most likey a stone for $10K from japan...)
I got myself a slate hone from ebay (from wales) and its not bad for the price. I also played around with thurigian whetstone (not an Escher, though)....