CDN Inc. v. Kapes

197 F.3d 1256 (9th Cir. 1999)

Kenneth Kapes's website has long since disappeared, but thanks to the Internet Archive, you can see what it looked like back in early 1998, before the 9th Circuit's opinion. CDN, Inc. is still around, and they continue to publish the same price guides Kapes subscribed to.

If you'd like to know more about collecting coins, also known as numismatics, start here. Once you've started, there are plenty of places to look up how much certain coins are worth.