Is there really a best time of year to buy?

I am in the market for a new car, but my old car runs well so there is not any sort of rush for an upgrade. I gad a dealer tell me the other day it was near the end of the month so they'd be more likely to cut a deal and others have said end of year is best as they try to clear out the previous years inventory. Anyone with more car buying experience know if there is actually a prime time to maximize deals when car shopping?