Best value to get US cash?

Mrs B and I are travelling to the USA in 10 days time. We have sorted fares, paid for accommodation and other items (tours, rental car) and have put some money on a travel debit card for use while we are in the country.
We now want to get some cash and with the recent drop in the value of the A$ I want the best bang for the buck I can get.
What is the best method to change A$ for US$ and get the best exchange rate and the lowest fees! We will be changing about $1500. All advice welcome, with thanks.