Originally Posted by JimKW
The best you can do is find what other cars similar to yours are selling for in your area. Problem is the dealer will give you wholesale value wich will be much lower than selling price.
The way to get the best deal is to sell your car yourself. I have used AutoTrader many times to sell cars. When you go to buy a new (or used car) you will get a much better deal when you do not have a trade in.
This ^^^^. You can find out what your car is approx. worth using the various methods mentioned above (ie, KBB, edmunds, private party sale in your area, auto trader, etc.) and subtract another $1500-3000 from that. That's probably going to be close to what you may get from the dealers.
Be patient. If you have a "good" car, someone will pick it up privately and you'll get more than what the dealership will offer. The fastest I've sold a car was in 5 days. The longest, approx. 3 months. And have gotten much more every time than what the dealerships were offering.