check out the scene in 'beyoglu' at night. for clubs and have drinks at 'cicek pasaj'. there are great 'meyhane's (traditinal places where turks drink) in 'kumkapi', where some classical turkish music could be heard.
usual 'tourist places' are not something to skip in istanbul. you can't anyway because there is something around every corner.

this week in istanbul they are expecting snow and it is rainy right now. suit up.

also, look into this expat site.link

Go for a cruise on a super-yacht, the islands are charming.

blue mosque

- agia sophia
http://www.greatbuildings.com/buildings/Hagia_Sophia.html

-Yerebatan Sarayi

http://www.balsoy.com/Turkiye/inpictures/si/Istanbul.html

I'd highly recomend reading "memories and the city" by orhan pamuk before going. that should give you some good history and background on the area, from the viewpoiont of someone who lives there.

pamuk is a fiction author, but studied architecture and art before jumping to words. the book is partly his memoir (intermixed with all this other stuff), but it's a good read. his fiction is nothing short of incredible.