The most "loaded" period in New York is the period between the Thanks giving day and Christmas. Beside the opportunity of taking a look the decorated tree in Rockefeller Centre, many come to New York simply for shopping.
About 11 million people visited New York the last year, in the period between October and December. Despite the current financial crisis, this year Manhattan won't miss the millions of tourists hastening across its streets.
It's natural, because such giant shop as Macy's, for example, are massive magnets for tourists. Moreover, during this period, almost every shop will offer considerable discounts for its products.