Well seems like we're headed towards 1929 again yah? If more US Banks collaspe, more companies will have no money. No money means no payroll for employees, means no comsumer spending, which will ultimately lead to less spending. Again, this will mean the consumer sector will fall (Nikon/Canon and all your other luxury brands as well) and the whole economy will spiral down.
The key fact is that the US is the biggest importer of all kinds of rubbish and if they stop doing so, all countries trade exports will fall and deficits will increase.
Of course all those gurus who claim that China and India will prop the global economy up are wrong. All the stuff produced there is by US companies and are probably exported there as well.
Anyway what central banks can do are just play with the interest rate, or money supply. Liquidity is in such short supply that Banks in the US are not even lending to each other. Hence the need to inject excess liquidity into the system to ensure enough cash to prop up the system. Of course the other way will be to slash interest rates to make borrowing cheaper, but that will again lead to another Japan, which by the way, still hasn't fully recovered from their own economic melt down.