How do I determine the value of a car?

I search Searchtempest, Craigslist, and Ebay to use those as comps. I don't trust the last one as much since it doesn't usually give a good representation. You also have to keep in mind, those are asking prices, not always getting prices. Sometimes things sell too cheap on Ebay due to wrong time of day for the auction to close or some times too much when people run up their own bids; unfortunately it does happen.