car's aren't selling at their book prices in this economy. if you're a private seller, plan on getting about trade-in value. dealers can get about private sale value.
instead of holding blue/black book value as a true going value, i suggest going to autorader.com and checking out listed prices. however, many of the cars are overpriced (book prices) and will not sell.
a better guide is to go to ebay motors and do a search for your vehicle. then, when the search is done, on the left side, there is a link for completed auctions. click on this and it'll give you a list of what cars actually sold for.
hope this helps.