I have always been a fan of Buffalo Exchange; the prices and the quality of apparel is truly unmatched. Although the customer service can be hit or miss, I would recommend Buffalo to anyone as a buyer.
As a seller, however, I would not suggest to most: they are highly selective about the clothes they take and will often take just the most obscure and unique apparel. Nevertheless, it's still a great store and I will be frequenting for years to come.