I'll keep this short and to the point...
I went to CarMax to get an appraisal for a car I wanted to sell. I chose CarMax because I didn't want to go through the process of posting a listing on Craigslist, Autotrader, etc. My thought was if they gave me a good price I would sell my car on spot. The service was quick, they have a very friendly staff and the appraisal took 15 minutes. I was expecting the appraisal to be ~50% of what I had previously valued my car (using KBB and Edmonds), they blew me away and offered 80%.
I couldn't have been happier. I'll definitely refer friends/family to CarMax as a great way to sell cars.