In Fifth Grade I wrote a poem about Madison Avenue.
Even then I sensed that there was something curative about walking past the stores with art gallery windows and watching the people go by. Years later, it's still a great way to spend a sunny day and, during sale season, it's one of the best shopping experiences there is. Unfortunately the big sales happen only about twice a year (January and July), and the rest of the time the great-looking threads in the windows are likely to cost as much as New York rent.
Enter Century 21.
Century 21 is a zero-ambiance discount mall near the World Trade Center site. Shopping here is a distant cry from the tree-speckled pavement of the Upper East Side. However, this is where you get the real deals. High-end outerwear, designer gowns, super expensive jeans, not to mention ties, shirts, shoes, sweaters and underwear - all significantly reduced. You may not be able to find everything you would ever want here, but if you have the patience to sift, you're guaranteed to find some gems.*
PS- Truly adventurous bargain hunters should check out Woodbury Commons, one hour away from the city. If Century 21 is a discount designer candy store, Woodbury Commons is Disneyland.
*If you're into seeking out gems, you'll find plenty of them in my book (slash Mother's Day Gift) "Secret New York," where I've already done all of the sifting for you.