Here is the link for the hotels in Istanbul

http://www.booking.com/city/tr/istanbul.en.html?aid=312627;label=tr-istanbul-xz6WHpnYd3e0e*8pFmbRnQC845291566;sid=2f9fdda035ac775a1507199eb86f4d17

Some other good links are:

Hotelopia

Hotels, hostels, guesthouses and appartments

www.turkeytravelplanner.com is also very helpful.  I have used his recommendations and have never been disappointed.

http://www.tripadvisor.com/Hotels-g293974-Istanbul-Hotels.html

It is always quite useful to check out the reviews from other hotel guests of a particular hotel so you can make an informed decision, and avoid nasty shocks!!

It also gives you details about places, night lift, does and dont´s etc etc and these are all visitors comments.

I have found it useful in the past and have also contributed with reviews of my own.