If there is any store in Stockholm you should visit it is Stockholm Market. Stockholm Market is a beautiful store in the center of Stockhom (Riddargatan 2 and the shopping mall MOOD) that has a lot of different brands to offer. In there you have everything from Alberta Ferretti to Jason Wu and Swedish brands such as Ida Sjöstedt and Dagmar. I can promise you that you will find a lot of things you like in there and if you are unsure of what you want the staff will find something for you. If you have the chance to go there anytime soon you will be just in time to have a look at the new collections and shop a little bit of the previous ones at the same time.
Visit it if you can, it is a pearl of Stockholm.