The first thursday of the month
At the first thursday of the month the Hermitage is for free. It was very crowded when i was there at this first thursday of the month but mostly it were tour groups so i seriously doubt that it will be less crowded in high season if you pay the normal entrence fee. Which is 200 rubbles at the moment (2005) which is not ridiculously high. The only thing i wished i had done was to be a bit more prepared in advance so i would know exactly what i wanted to see. Now we just got lost every time since we just turned at every thing that we found interesting looking. Which was a lot of fun, but also made us miss out on some seriously interesting stuff.