AutoSite
Looking to buy or sell a new or used car? Get the buying or selling price by model, year, mileage and options all for free! Also check the vehicles history by vin number and get vehicle recall lists.
Kelley Blue Book
If you are going to Buy or sell a used car, this is one site you do not want to miss! Offers all the above features for free, plus a more detailed car options list. It also gives you a basic trade in value estimate.It's a great guide!
Edmunds
Another great car pricing/advice guide! Lots of options!