In NYC, the most logical zone would be Manhattan south of 60th Street, since this would cover all 4 free East River bridges as well as people coming from the north of Manhattan where there are free bridges from the Bronx.

The most comprehensive and compelling analysis I could find was put together by Jeffery Zupan of the Regional Plan Association. He reviews 4 different options for congestion pricing and the impact it would have on the number of cars, trucks and other vehicles entering Manhattan as well as the increased mass transit ridership.

However, this is politically unpopular for politicians in the outer boroughs. We need to convince them that this is the right thing to do for the whole city. I think dedicating those revenues to (A) Regular Maintenance of the Bridges (B) Alternative Fuel Stations - biomass/ethanol, electric, hydrogen, etc (C) Upgrading bike lanes, etc. For the electric train cars we need to talk to the MTA.

From a peak oil perspective, this type of policy would help transition our economy so that when gas prices start to run away, we already have changed commuting habits in such a way that the impact will be less chaotic.