The No. 1 cost that new car owners face is not gas, maintenance or insurance, but depreciation, Quincy says. If you buy the 2010 model that's still on the lot at the end of year or remaining on the lot at the start of 2011, it's already almost a year old. Even though it's a brand new car, it's already depreciated in value, he says.

"A leftover model, in general, can be a good deal if you're the kind of person who drives their car into the ground," Quincy says, noting that could be 100,000 to 200,000 miles.

"If you like to buy a new car every two to three years, the car already has a year's worth of depreciation."

On the other hand, some redesigned models hitting the showroom floors later in 2011 are not as good as what's still on the lot, which would give you another reason to go ahead and buy a past model.