This chart shows the mean sales price for domain names of various lengths. The numbers in the X-axis indicate the number of characters in each name, excluding the TLD. As you expect, there is a steady decrease in value as the number of characters increases. What is interesting however, is the pronounced dip that occurs at 4 characters and the plateau from 5-8 characters. When choosing a domain name to register, 5-6 characters is your best bet.

This chart shows the mean sales price for domain names broken down by categories. Although there is no single category that shows extraordinary value, it can be seen that names with general applicability (G) are twice as valuable as names relating to special interests (S).