I find a good method is to buy currency from my bank before I leave. Specifically, I have an account at Bank of America, and for a $7.50 fee they will convert currency before I leave. I believe they waive that fee if you convert more than $1000 USD.
I also bring some US$ along with me in cases of emergency. I don't want to bring my own ATM card with me on business trips to high risk countries because I don't like bearing that risk myself.