For Petersburg...
There's not much readily available beer that's good in Petersburg. I found one "brew pub" that even did take aways in plastic bottles, but it wasn't real great.
There's a large variety of slightly different local beers, and you can have fun seeing if you can tell them apart, but basically just go to Dumskaya and drink whatever they've got:
http://www.openstreetmap.org/?lat=59.93 ... 8&layers=M" onclick="window.open(this.href);return false; (If you're into dirty rotten awesome bars)
Some great bars though... any of the bars on Dumskaya, or try and get to a show at the Griboedev. (It's in a old bunker)
Lenta, a big (pricey) grocery chain has an excellent selection of imports though...
If you visit Liverpool, it's run by an Icelander, he normally likes some company...