In the summer, Istanbul nightlife move to the shores of Bosphorous. Unique to Istanbul are the ‘superclubs’ which are kind of entertainment complexes under the same roof (well under the same sky as they are open air) They have restaurants, bars and a club which makes them a great place to go early at night and stay until the early hours of the morning. Sortie have regular events, concerts, cinema showings, especially on Sundays so it’s worth checking their website from time to time.
Reina: www.reina.com.tr
The oldest of these clubs, and after years still the most popular. It has a number of restaurants in including Turkish, Seafood, Chinese, Greek, Italian, 2 bars and a large dance floor. It is situated in Kurucesme by the Bosphorous and have wonderful views. For early evening drinks, the place is quiet with a chilled atmosphere and music. It is not a time for people watching and posing.
Dinner service starts around 830 (starts earlier but would be empty) and continues until about midnight, some of the restaurants are for late night eats and stay open all night. I can recommend Kosebasi for a good Turkish Kebap, or the new Greek restaurant Varaulko by a famous michelin starred chef.
If you want to go just for the bar, unless you have reservation, or buy drinks buy the bottle, or know the manager, or pay a huge tip, you cannot sit at the tables but have to stand up around tall bar tables or around the bar. Even if you are standing in a corner, it is waiter service though. Waiters find you anywhere, bring your drinks promptly and get their payments. It is very efficient. The bar areas become a club later in the night, around 1am. There is a dance floor and resident and visitor DJs play a mixture of Turkish and International hits. The music is very middle of the road, aimed to please everyone as people from all age groups visit Reina.
Reina is expensive. Drinks over £10 per cocktail. Food depends on the restaurant. The doormen have been critisized as being rude. I’ve always been to Reina for dinner and then stayed on late so did not have deal with the doormen as having a reservation guarantees your entry unless you are so under-dressed and scruffy that they may refuse entry.
Reina is full of posers, people with money there to show off as in many top clubs around the world. If you don’t like that sort of thing Reina is not for you. People, especially women are really dressed up and I like going to Reina even for the people watching. Not many people dance but sort of shuffle on their feet which is funny to watch but a lot of people let their hair down and have a great time as well.
The views are breathtaking and if you have the budget, spending a night out in Reina would be a great experience that you won’t forget easily. If you don’t have the budget, you can still dress up, come to Reina around 730 – 8 and have a cocktail and watch the sunset surrounded by the beautiful people of Istanbul.
Reina is also open in winter but offer limited service indoors with only the Reina restaurant but is is still very popular with a late night bar and club.
Sortie : www.sortie.com.tr/
100meters from Reina, it is very similar in style and concept so I won’t repeat the general features, you can refer to what I said about Reina above. As posy and expensive as Reina and as difficult to get into late at night. 
It has many restaurants including a good Turkish restaurant, Japanese, French, Brazilian, Chinese, International cuisines as well as a wonderful Fish Restaurant. I would highly recommend the fish restaurant Fishmekan. Most of these restaurants have their main location outside Sortie as well and I like Mori, Mirror and Sahan.
Suada (water island) : www.suada.com.tr/en-US/
Suada is really special. It has a unique position of being an artificial island in the middle of the Bosphorous. It used to be a sports club but for a couple of years its’ been rented out as a pool/bar/club complex.
During the day it operates as a beach club with an Olympic sized pool. You can only imagine the wonderful panoramic views of Istanbul on all sides, being in the middle of the Bosphorous. You access Suada with the complimentary boat service from Kurucesme. You pay entrance fee for the pool and can enjoy it all day, with happy hour drinks in the afternoons on Saturday and Sundays.
In the evenings it is very similar in concept to Reina and Sortie (see above) 
The place has many restaurants including a cafe, Italian, Turkish, International and Seafood. Mezzaluna, the Italian restaurant have many branches around the city and is very good. I would try tor Turkish Kebap restaurant as well, you can’t go wrong in this stunning location. Suada has a number of bars and it becomes a club alter at night.
I would highly recommend Suada, for a day out, evening drinks or a full night out just for the unbeatable views of Istanbul. It hosts regular ‘beach’ parties during the day and have many performers such as Ayhan Sicimoglu and Latin All Stars, a Turkish Latin band on Wednesdays (they play at Reina on Sundays).
Dresscode
Dresscode for all these clubs at night is similar. Unfortunately you need to look the part of you want entry to these clubs, especially late at night.
Women dress up. Revealing dresses, short skirts, skimpy tops all acceptable, even expected. Top labels, expensive bags, strappy high heeled sandals, jewellery, you can really go over the top. In the summer colourful dresses are seen as well as black dresses. A minimum would be nice jeans, a sparkly dressy top and high heels. You will not see a woman wearing trainers or flat shoes. You’d be surprised how many girls have their hair done, at least blow-dried and there is lots and lots of make up.
Men usually wear jeans, black cotton trousers and a smart long sleeved shirt. There are some younger men with smart designer t-shirts. During the week there will be men in suits but only if they are coming after work, suit and ties are not needed and not seen on weekends unless coming from a wedding. Oder men wear tailored trousers, a crisp white shirt or polo shirt and sports jacket. Lots of linen is acceptable, similar to Italy. Very smart trainers are sometimes acceptable if you are a trendy youth but you may be refused entry.
Transport
The traffic around these clubs which are only hundreds of yards apart is horrendous between 9pm – 3am. Police is doing their best but when thousands of people arrive in their cars to be valet parked this is difficult. Taxi is the best way and taxis wait outside until early morning. Of course the only socially acceptable way to get into Reina is by your own Boat :-) but this may not be an option for most of us.
Have fun in Istanbul !!!!!!!!!!!!!!!!!!!!
UPDATE (Oct 2011)
I was in Istanbul last week and we went to Suada, to eat at Suada Balik and it was a great night out in winter as well as in summer. The weather was quite good for October so it was semi-open but with lots of heaters and we had beautiful mezes and lufer (bluefish) which is in season right now. There is also Suada Kebap and another seafood restaurant still open, as well as the bar. The boat trip was quick, again heater in there so don’t hesitate to go to Suada in winter

The summerclubs in Istanbul are great, can’t wait for next year. Which winter clubs do go to in Istanbul?