I use truecar primarily to find the invoice and work from there. Also know if you belong to Costco they have a car buying program that is typically a good bit under invoice. Easy way to get under invoice without having to haggle.
I belong to the scca so I can get a VW (possibility Mazda but haven't checked those details yet), for $500 under invoice no haggle. I'm using that on a car I've ordered since I won't have much bargaining power on it (rare model built to my specs, would sell easily if I wasn't primary on it). Sadly unregulated dealer fees in my state mean I basically lose my discount, but better than MSRP!
FYI, to anyone looking at VW scca is ~$80 a year, so joining can pay off if you want a quick and easy deal. Also know that several negotiate the car down to under invoice and then use this certificate to get another 500 knocked off because that money is refunded by VW to the dealer, so they don't lose anything. I had originally done this with a couple cars to get $1k under invoice, but supply problems meant I lost 4 cars and ultimately settled on ordering exactly what I wanted.