Selling to someone who knows the car and the care it has recieved is usually where the best value is for both parties offering quick and easy logistics with both sides of the deal fully informed. Most of my cars have sold to nieghbors. One went through at least two generations and is likely worth more today than when I sold it (1967 289 Mustang GT fastback, manual transmission). Everyone came out happy.

If you do not get it worked out locally, Edmunds.com can be helpful in determining private party values based an actual sales rather than inflated asking prices. In my state trading in also offers tax related benefits often not fully appreciated and should be considered.