Edmunds , a favored auto authority since before the Web, has an excellent informational site. But at Edmunds, you get more. Dealer holdback is a percentage of the MSRP or invoice of a new vehicle that is paid to the dealer by the manufacturer to assist with the dealership's financing of the vehicle. It is almost always non-negotiable. Knowing the holdback, however, can sometimes be a negotiating tool.
Every automata has one or more.
These are excellent places to get vehicle specifics and a good pictorial look at the vehicles you're considering. They allow you to identify what kind of vehicle you want to buy and configure it to your needs. The dealer will typically call you within 24 hours. These sites are basically online brokers. They consummate the transaction online, guarantee the price to the consumer, then farm the sale out to their dealer network.