I bought a car last year through carsdirect.com. Well, almost.
I had carsdirect find and quote me at invoice. Then the dealer that was working with carsdirect.com called me directly and offered it at $500 below invoice. I agreed, they drove the car to my house, I signed the paperwork and it was the fastest easiest car buying deal I ever made. And even included 7 yr/100k mile extended warranty for free.