With their exorbitant rates, Manhattan parking garages will scalp you, then use the bloody hair-hank to buff someone else's Benz. To get the best deal possible, try NYC Garages.
NYCG's a free service that aggregates info from 1100 auto motels, then grinds through the numbers to present a thorough price comparison that'll amaze and disgust you. Choose to crunch daily/monthly rates, incorporating variables like early-bird/evening/holiday specials, overnight charges, even vehicle type -- compact, SUV, exotic, chauffeured, and, if you're Al Gore, electric. Just define your location by address, intersection, neighborhood (from the Financial District up to the "coming soon" 100s), or civic attraction, and your info comes out plotted on an interactive Google map complete with rollovers showing you who will gouge you only slightly, and who will screw you to the bone.
Even if you don't own a car, the site can help you help others, like clients driving in from New Rochelle, or John Madden. Hopefully, version 2.0 will add shady attendant profiles, with warnings like "careless", "vindictive", and "steals mixtapes". Oh, and "will launch your friend's dad's classic Ferrari into the air while you're off playing hooky".