2nd and 3rd gen iPods are totally different animals. The 3rd gen is the only one with the 4 buttons above the touch wheel and are backlit in red. As far as value, a 40GB 3rd gen and 20GB 2nd would probably be the highest value. At this point, there really isn't any book value on it anymore, so the only way to find out would be to list it for sale and see what offer you get.