Mustard Seed is the sort of place you maybe don't realize exists, because it is too good to be true. Designer second hand, for next to nothing? They generally, on a good day (which is mid-week, mid-day if you are over a size three, or size 6 shoes) have designers ranging from J.Crew, Calvin Klein, BSBG, you name it--for under twenty dollars. Often a sweater is ten dollars or less. Avoid the clothes in the front, they are brand new retail priced, and go straight to the middle where all the good second hand designer finds are. Also to avoid: they now have a "vintage" section, which while some of the clothes are lovely, is just a way of bilking the public out of money by jacking up the price and claiming its from the 70s, etc. Its not worth the added price. But otherwise, Mustard Seed is a dream. Low prices, good finds. Highly recommended.
They also will buy your clothes if they feel they are "in" at the moment (and weather appropriate). You won't get much but it is a good way to clean out the closets.