AutoTrader.com and Edmunds.com announced Monday that AutoTrader.com will provide used-car info for shoppers on Edmunds' site, the companies said in a statement. Through this partnership, shoppers now doing their research on Edmunds.com can click directly over to AutoTrader.com's massive inventory of 2.5 million used vehicles. And those who use Edmunds.com's True Market Value Used-Vehicle Appraiser to determine the price of a used vehicle they intend to sell can now easily their vehicle for sale with AutoTrader.com. AutoTrader.com, headquartered in Atlanta, Ga., lists more than 2.5 million new and used vehicles on its site. Edmunds.com is a Santa Monica, Calif., company that has automotive research, reviews, pricing and data services on its Web site.