Deniz Gokce: Excellent tracking of current events (Turkey and world)
Serhat Gurleyen: The only one in the list I've met, and he really impressed me as very knowledable and thoughtful.
Salih Neftci: A must-read if you would like to familiarize yourself with the tools and instruments of modern finance. I wouldn't put my money on his predictions though; he likes to make specific forecasts, which are not likely to be exact all the time.
Hasan Ersel: Shows that asking the right questions is usually the most important step in reaching the answers
Ercan Kumcu: Knowledgeable ex-Central Banker, with somewhat an international macro focus
Haluk Burumcekci: Chief economist of Fortis, one of the few Turkish market economists I really trust.
Seyfettin Gursel: While his main expertise (and the main reason I follow his columns) is Turkish labor markets, I find his politics pieces interesting as well.