Japanese whetstone manufacturer Shapton produces some of the hardest whetstones on the market. We have imported two series from Shapton: Glass and Kuromaku. We are right at the top of the whetstone world regarding quality.
Shapton's stones are "Splash and Go" stones, which means they only need a little water on the surface, and you can start sharpening. Both sets of stones have proven in my tests to be of very high quality and easy to use.