Concept Carz is one of my favorite tools for collectible car values. While it does not cover every car, the important thing is that Concept Carz gives you FREE access to auction results that other websites charge for. Auction results are given in year-on-year summary, but you can also drill down to view individual cars at specific sales. 

CAR GURUS is one of our most productive advertising venues. Their tools allows you to get an IMV (Instant Market Value) for your car based on the VIN or make, year and model. The IMV gives you a statistical market value based on the mean of all their comparable advertised cars. It is most useful for late model cars that trade in good volume, less useful for vintage or thinly traded car. 

The Hagerty Valuation Tool allows you to search collector cars by year, make and model. We consider Hagerty's values to be among the most reliable and the guide itself quite easy to use.

NADA is the National Automobile Dealers Association. They have sections for all types of cars, trucks and motorcycles that are easily searchable. 

Sports Car Market is the premier magazine covering the market through auction results. Their guide opens in a viewer which you can navigate as your would a printed magazine.