There's a local store here in San Diego that specializes in selling/reselling Apple stuff, they're called Quality Macs. You can check them out at qualitymacs.com or go straight to their business arm that does the quoting for used gear, at cashforyourmac.com and create quotes for a variety of items. They lock in the offer quote for 30 days and supply a prepaid FedEx shipping label. I've been dealing with them for years, selling my (gently!) used Apple stuff to them.
Not sure how competitive the prices would be compared to other places, but they have always offered better than what Apple ever has, and the no muss no fuss process is hugely convenient to me. Create a quote, drop it off at their store, get a check in the mail a few days later. Having to deal with the huge potential for hassles when trying to sell Apple stuff private party is just not worth it to me to get a few more bucks.
Check them out, I can personally attest to them, and their online or in person customer service has been nothing but stellar.