We seem to get a lot of questions on the forums about what is a good price for a vehicle. I just heard about a new site that will let you plug in the vehicle you want with the options you want and compare what people are paying nationally, regionally and locally. It also will show you dealer cost, factory invoice and trends over the past 6 months.
TrueCar collects and analyzes data from 25% of the automotive sales in the US so its not every sale but the site may be useful in addition to sites like edmunds.com
http://truecar.com/release/index.html