Possibly one of the best markets in the city to find knockoffs of almost anything found at the department stores or boutiques in the Kangnam area, at a fraction of the price! The Doota B/1 is a great place to find such products. Upstairs is a great place to find accessories and their shoe department has almost the same shoes as available at the Galleria at one third of the price. The quality is somewhat questionable and the styles are sometimes not as good as their more expensive counterparts, but nevertheless, they are great hit or miss places.
Chain stores such as the Chunghap Sijang or the Dongdaemun Chain Store are great if you are looking for supplies to make your own stuff. With everything imaginable under the sun, it is great for supplies; however the tailors there don't speak English. The fifth floor of this market sells beads and chains for necklaces and it is a great place for the creative fashionista.