I usually park at, and can recomment, Vinci Aeropark. They have one stop at the Sheraton on the way to the terminal, and on the way back they suffer from the problems everyone else does, too, because of the current construction spaghetti roadways.

You can get 20% off by simply asking for a coupon at the gate (I suppose it is best to ask on the way in to use on the way out) and the base weekly rate is $60, so that makes it $48. For $5 more they will put the car in the VIP section and have it clear of snow and ready to go for you when you arrive. Best to call from the terminal when you have your luggage.