I am a brit that emigrated to the USA only 4 days ago and am currently living in SW Florida.
My advice would be to do all of your banking with Citibank.
I opened a sterling current account with them 5 months ago, which I had my wages paid into. About 1 month ago, I also opened a US Dollar current account with them. The beauty of this is that you can transfer money using internet banking directly between accounts. It is instant and you don't get charged commission for it and also it is at the banks exchange rate, not the tourist currency rate (currently 1.945 USD = 1GBP).
You are issued one debit card that is used for all of your accounts. What you have to do is call citiphone banking and nominate which account you want the debit card to work for.
Once in the USA, if you buy anything or withdraw cash from selected ATM's (check
www.citibank.com) you are not charged any commission and it draws directly from your USD bank account. All you have to do is keep the account topped up from your sterling account. Apparently the money clears through New York, so it a lot quicker than normal.
There are certain restrictions, one of them being that you have to have at least £2000 in credit at any one time in any one of your accounts, or you get charged $20 per month for the USD account.
Citi also have a great high interest savings account which you can keep your cash in and transfer from/to.
Another bonus for me was that I got a free ipod Nano for opening the account, but I am not sure if that offer is still running.
You can apply for an account online (just go
www.citibank.co.uk).
They have several branches in central London.
Hope this helps. I think it is definitely the best way to go !!