Costco (supposedly) has pre-negotiated, no haggle pricing. I used them in the past, and the experience was great (except for the trade-in). Also, there are still car brokers that you can hire to do your bidding.
I really don't know much about them beyond my own limited experience as a shopper (about 6 years ago). I came to know of a local broker (southern California) via a referral at about the time I was looking to buy a new car, and decided to try the service. This particular broker charges an up-front, fixed fee (maybe $100? I don't remember), and he shops for the best deal in the region for your specific vehicle configuration.
Even though I hired him, I decided to also see what the local Costco deal was (wasn't completely confident Costco couldn't do better). The pricing the broker negotiated was a shade better than I could get through Costco (maybe $75 less, including the broker fee), but the big plus was that the car was delivered to my door, and the contracts were signed on my kitchen table. I never had to set foot on a dealer lot (minus my own Costco experiment). No "finance guy" circus. It was cleanest car buying experience I have had.
