Buenos Aires: This main street starts not far from the train station and extends right through to the heart of Milan. This is the street filled with local boutiques, Benetton's and Stefanel's, and cafes and fast food. I always start here first, and manage to find good prices for clothes and shoes.
Monte Napoleane: This is the famous street where expensive name-brands such as Gucci and Versace reside. There is also a brand new Armani store which fills up the whole block. I personally would stay away, it's a disappointment. It is nothing more than a small street with big names. I would venture to the surrounding areas instead, where you can still find high quality but more interesting items.
Piazza Cinque Giornate: This is where a huge Coin department store resides. Have a veal milanese for lunch at the top floor-there are many local Italians dining there, not a tourist in sight. The streets surrounding the piazza offers many shops.