You will never feel wealthier than when shopping in Buenos Aires. The exchange rate makes everything here seem so cheap and reasonable that it literally makes sense to buy everything you think you will need as far as clothing goes for the next couple of years. I think that the exchange rate is still at about 1USD to 3.3pesos...meaning that you essentially get to divide the price of everything by 3.3 if you are coming from the states...or by about 7 if you are coming from the UK. It's ridiculous but an incredible deal.
What makes this such a good deal is that Buenos Aires has a number of international brands. You can buy products that would cost you significantly more in the states for a fraction of the price. I got a full suit (with complimentary tailoring), dress shirt and tie at Christian Dior for $280. I saw nearly the same suit available online in the states about 6 months after I got back for nearly $2000. If you are about to buy an expensive suit in the states it would literally be cheaper to fly to Argentina, stay in a hotel for 5 days and buy the suit there.
Argentina is as huge on leather as they are on beef. You can get a custom made leather jacket in any color you like perfectly fitted and sewn to your liking for a few hundred dollars. If you find a leather jacket in the states that you really like take pictures of it and bring them with you and they will duplicate it for you in a couple of days. Leather goods are also available everywhere you go at a fraction of the price as could be found in the states. The best place to buy leather is in the area around Murrillo and Scalabrini Ortiz streets. Just ask when you get there or check out a map.
People in major stores and the leather district will speak English for the most part as a solid number of their customers are American tourists these days to don't worry about miscommunicating custom decisions if you are having something made or tailored.
There are many American style shopping malls in Buenos Aires that offer a huge variety of international and Argentine labels. The Alto Palermo mall on Avenida Santa Fe is one of the largest. Paseo Alcorta is another large mall that has a huge American style movie theater in it. We got a little tired trying to go out every night of our trip and this was a good alternative as it gave us something to do in the evening for a few hours. All the movies are in English with Spanish subtitles and the theaters are state of the art, more comfortable and with better sound and sightlines then most places in the states.
A lot of the malls have similar chain stores as the malls do in America. If you are looking for upscale boutique stores head to Recoleta where you will find a number of international brands. I didn't buy anything from this area and therefore am not sure if things here will actually be cheaper than the states but it would definately be worth checking.
All in all Buenos Aires has some great deals and if you are in need of clothes this is the place to get them. Buenos Aires also has great deals on household goods and virtually any other items you are looking to buy. And ask for a tax refund receipt on any large purchases at major stores. All shopping is tax free for tourists in BA. You get all your tax back at the airport when you are leaving on any purchases over like $50 or something. I don't remember the exact amount but almost everything we bought qualified. Just ask at the store.