I'm headed back out UK > US next weekend and still have my currency card from my last trip. If you're not familiar with these currency cards, you 'load them up' via online bank transfer and then you can use them to pay for things/withdraw from ATMs in places like the USA. Unfortunately, the £GBP to $USD exchange rate they offer is shocking (like 1.63 dollars to the pound, over say 1.67 at most local exchanges as of 01/06/14).
I don't suppose there's any better deals out there at the moment?