If we are talking about non-islamic non-historic places that are touristic, there is always the Bosphorus and the many seafood restaurants alongside that might fit the bill, provided that it's not raining. There are quite some modern museums and/or art galleries. A walk along Uskudar or in Beyoglu back streets is safe and quite fun. Beykoz is very nice also. The night life is quite lively, and that could be considered touristic. And yes, there are many discos, although the season is getting a bit long for some of them, but on weekends they are crazy enough you won't notice. Some of the more exclusive discos/night clubs can be a bit steep though (you'll get the hint when you are about to walk inside, all those shiny porsches and whatnot). I do not recommend the beaches, it is getting a bit cold, although you might try your luck in Kilyos.
