Big Data Labs has released Vinny, a free app that instantly calculates a car's wholesale price. Just type or scan in the VIN number, and Vinny magically loads information about the make, model and estimated price.
Adjust the miles, set the condition, and Vinny updates the typical transaction price. You can also see the retail value and request insurance quotes.
It's a cool little app that we've been all testing on our cars here at TUAW. You might want to check it out as well. For what it's worth, my 12-year-old minivan has held far more value than I ever imagined.