Edmunds seems to have fairly accurate invoice prices. But you can't expect anything but slow sellers to trade at invoice. I think it is better to visit one dealer and get a price, and then visit another across town and get a price on an identical car (same options and everything). Then, ask one guy to beat the other on the price. When he responds, notify his cross town rival and tell him that he was just beat. Keep it going, and eventually you'll get the car at market value (i.e. the lowest anyone is willing to sell the car). I did this over the phone for about a week when I bought my Crossfire coupe, and I got it new for $24,500. Sticker was just over $30K. But this is a Crossfire, which sits on the lot far longer than any dealer would prefer. It had yellow stickers on it, indicating it already sat on the lot far longer than it should have.

On, say, a new Solstice, you will not be getting it anywhere near invoice. That's not "unfair". Dealers are in business to make money, and they will do their best to perform at or above the market level. Besides, I enjoy the dealing side of car buying. It's fun, and if done right, everyone should feel good about the results (buyer and dealer included).