I ran across this while surfing. To help everyone avoid buying stolen macs, powermax.com has made its database of the serial numbers of stolen macs available to the general public.
They posted a disclaimer that if you don't find the serial # in their database, that doesn't mean the item isn't stolen. But anyway, it might help.
If anyone else has found similar links, it would be great if we kept them available here.
Coconut Identity Card can search online databases for stolen macs. The only thing is, you'd have to have internet access and the seller would have to let you install the software. If it's an ipod, you can plug it into your laptop and check.