We stayed at The Witt Suites in Beyoglu last November. It was a special trip and so we booked the Penthouse room for EUR429. The wrap around terrace had a full view of the Bosporus and the Golden Horn. It was quite possibly the best view I've ever had in a hotel. Full breakfast was served every morning on the terrace. Lord I could have sat there all day, it was that nice. The front desk staff was really helpful, very friendly, and quite good looking

They run a nice blog that I found to be pretty helpful:

http://www.wittistanbul.com/magazine/

Can book online at http://www.wittistanbul.com

Can't say enough about the place - would definitely stay again.