Amazon definitely has the best deal to trade in, for my 3rd generation iPad 32gb they are offering $460.00 credit. Im sure though I can get $500 for my 32gb if I sold it on craigslist though.
i also wanted to say that I never gauge the price of my Apple devices by seeing what they go for on Craig's. In Charlotte, NC, the majority of listings of Apple stuff is from spammers and scammers. It's sad.