That Norton link has the best prices I've seen.
I use Norton, Shapton, and King. They all work great, but the Shapton stones cut fastest and leave a great finish. King stones cut the slowest, but leave almost as good of a finish as the Shaptons. The Nortons are in between for speed and finish, but their finish is also top-notch.
JWW has the best price on Shapton Pros.