If you're interested in a Private tour of St. Petersburg I can recommend the services of Tatiana.
We used her services and found that she is a friendly, reliable and interesting guide.
Best of all - she will made a customized itinerary for you - so you get to visit the places you most want to see. Especially important if you have limited time.
She has a website
wher you will find further details and information on how to contact her.
I wish you a wonderful time in this beautiful city.