Currently perusing a copy of 
Modern Nishikigoi: Basic Varieties and Unique Koi
. This book is great for the beginning koi enthusiast. It describes in great detail the 3 most popular types of koi (Showa, Taisho Sanke, Kuhaku) and describes characteristics of many others. There are types of koi in this book that that are possibly now extinct or are not being bred for the US market. The book is loaded with photographs of good specimens of each type. The descriptions illustrate what qualities to look for as well as those that are less desirable (from a judging standpoint). There is a great deal of knowledge about how koi are judged and ranked within each of the major categories. The book was published in 1986 so may be a bit out of date but you can see how modern koi have evolved even from 30 years ago. There are still some copies on Amazon (click the book cover) if you are interested. I may list mine or save it to give away in a contest later.
UPDATE: My copy is now listed on Amazon.com for $32. If you wish to buy it direct from me I do accept paypal and will ship within the USA. If it doesn’t sell by Christmas 2011, I may offer it in a contest in 2012.
