They also have a Used Bike Value Guide that's a handy reference point when you're perusing the craigslist motorcycle classifieds. It's not surprising that the majority of motorcycle owners are asking more for their used bikes than the NADA price.
The NADA prices are for the "full retail value of a stock motorcycle in a reconditioned or clean, undamaged and well-maintained condition with average mileage, ready to be sold by a dealer or between individuals. The value assigned is a national average." These prices are a good starting point for determining if that craigslist bike is a good deal or not.
It's not online but Motorcycle Consumer News also has a summary of every popular motorcycle showing 0-60 time, top speed, horsepower, torque - if you like to compare those things.
I'd guess Motorcycle Consumer News probably appeals more to a mature rider, or someone who likes motorcycles, and riding motorcycles, in general and isn't locked-in on a particular brand or type of riding.
MCN is available at the Everett Public Library or you can get your own subscription for $22/year.