Pulkovo is the main and the only one international airport in Saint-Petersburg area. It’s about 25 km from the center of Saint-Petersburg. You can reach Saint-Petersburg from airport in 3 ways: bus, taxi bus (it’s Russian invention J) taxi.
Unfortunately there is no rail connection between city and airport, so in any way you have to use regular roads.
I strongly recommend to take ONLY official taxi. First because of the most fair prices and the second unofficial taxi ( in Russian language they are called “Bombily”) can simply because you are a foreigner beguile you out of money. The cost is varies on your destination but to the center of Saint-Petersburg it gona be about 800-1200 rubles (~13-20$). Official taxi price map: http://www.pulkovoairport.ru/en/transport/taxi/ .
Bus and taxi bus
I made equal sign between bus and taxi bus because they follow practically the same route. The difference is that taxi bus usually takes less time to reach it’s final station because they are smaller and they make stops ONLY by ask of a passenger. As for me for foreigner it’s the most inconvenient way to get to the city just because of the language barriers. In bus or taxi bus practically always no signs in English, no announces of stops in English and finally in most cases drivers don’t know English at all.
The Buses that you can take from airport to city (http://www.pulkovoairport.ru/en/transport/bus/ ) is: 39, 39A to Moskovskaya metro station. Price is 28 Rub (~0,5$). Travel time 20-35 minutes.
The Taxi buses that you can take from airport to city (http://www.pulkovoairport.ru/en/transport/bus/ ) is: K39 to Moskovskaya metro station. Price is 36 Rub (~0,6$). Travel time 15-20 minutes.