You search by the make and model and they link you to a gang of dealerships, they also have pics and details on the car on their main page before you click out of their site.
I don't like carmax, just because their cars are waaay over priced.
I'd check out Autotrader or ebay, carfax is a good resource for comparisons and so forth and always if you buy private check out kelleys blue book. If you are buying newer cars and from a private you can get the warranty tranfered so that is something to think about too.