I try to make it down to Housing Works every week to buy used books. They are an AIDS-related charity and I love that I can support my reading habit without breaking the bank and support a good cause at the same time. The atmosphere is unpretentious and casual, the store has a great cafe in the back and several shelves tucked up on old fashioned balconies. Unlike a lot of used bookstores, their bargain bins are filled with books that you actually WANT to read -- lots of the classics, in solid condition, usually not more than a dollar or so. A NY treasure.