If you want to do shopping there are several options. One of them is Nişantaşı street full of stores with local brands and foreign brands. Nişantaşı has also stores of Turkish famous designers. The second option is Osmanbey, which is close to Nişantaşı and prices are more reasonable. Bağdat Caddesi (street) also a big source for shopping. Fancy street with fancy stores. If you like shopping you should see Nişantaş and Bağdat streets.

If you want cheap shoppin places I suggest below:

1- Beyoğlu İş Merkezi – Taksim

It is located on Istiklal street. Really prices are very good!

The adress is  Adres: Asmalı Mescit Mh. İstiklal Caddesi No: 187 İstiklal Beyoğlu İstanbul

2- Terkos Pasajı – Taksim

This one is crazy place like open markez on Istıklal street. Cheap cheap cheap! You can find a tshirt for 5 Tl (2 Euros) Adres: Asmalı Mescit Mh. İstiklal Caddesi, Terkoz Çıkmazı Sokak, Beyoğlu-Taksim/İST

3- Beşiktaş Çarşısı Sinanpaşa Pasajı – Beşiktaş

This is located in Beşiktaş and if you ask someone, they will show.

Adres: Hasfırın Cad. Sinanpaşa İş Merkezi No:5 Beşiktaş

4- Opera Onur Pasajı – Kadıköy

This is located in Kadıköy on Bahariye Street.

Adres: Osmanağa Mh., 34714 Kadıköy/İstanbul

Also open bazaars can be a option.

Also there are big AVM’s in Istanbul. Below you will find them

Akmerkez Shopping Center

Akmerkez

This four-storey mall with almost 250 stores covers an area of 180.000 sq meters.

10 am and 10 pm every day.

Address: Ulus Caddesi No:3, Etiler – Istanbul

http://www.akmerkez.com.tr/

Istinye Park Shopping Center

Istinye Park

Spread out over an area of 242.000 sqm, the shopping center offers a variety of outdoor and glass roofed indoor sections such as a green central park, Fashion District, street side shopping, a kids’ entertainment center of 1.500 sqm, Hillside Sports and Leisure Club, The Bazaar — an area inspired by historical Turkish architecture — and 12 movie halls, one of which being IMAX 3D.

Address: İstinye Bayırı Cad. No: 73, Sarıyer – Istanbul

http://www.istinyepark.com

Kanyon Shopping Center

Kanyon

As a four-storey shopping center located in the financial district of Levent, the 37.500 sqm shopping center has 160 stores among which Turkey’s and the world’s most selected brands, gourmet restaurants, cafes, a health and sports club and movie halls.

Address: Büyükdere Caddesi No:185

http://www.kanyon.com.tr/#/en/homepage/

City’s Shopping Center

City’s

City’s concept is described as a Life Style Center. It sure deserves this stylish title, considering the variety of the stores, cafes, restaurants and the vital 24 hour six-storey parking service it provides to the populous area.

Address: Teşvikiye Mahallesi Teşvikiye Caddesi No:162, Nişantaşı – Istanbul

http://www.citysnisantasi.com/

Forum Istanbul

It includes big stores like IKEA, the sports store Decathlon, Praktiker, several technology stores, 62 domestic and international clothing and shoe stores, 15 cafes, 34 restaurants and 10 movie halls.

Address: Kocatepe Mahallesi,Paşa Caddesi, Bayrampasa – Istanbul

http://www.forumistanbul.com.tr

Galleria Shopping Center in Istanbul, Turkey.

Galleria Shopping Center

Galleria

It has several elite stores, restaurants, movie halls, a bowling hall and an ice skating rink. Galleria was recognized as the world’s most outstanding mall in 1990 by the International Council of Shopping Centers (ICSC) for sophisticated blueprint design, rapid construction, and unique structural features.

Address: Bakırköy Ataköy arası sahilyolu, Istanbul

http://www.galleria-atakoy.com.tr/

Metrocity Shopping Center

Metrocity

A four-storey shopping center housing 140 stores located in the finance district of Levent. Teflon coated fiberglass fabric was used for the roof construction, which brightens up the shopping pleasure.

Address: Büyükdere Cad. No:171 1. Levent

http://www.metrocity.com.tr/