I did a RTW trip recently and after some research came to the conclusion that a free checking account with Charles Schwab was the best way to get cash worldwide. It is a Visa card on the Plus network . There were only 1 or 2 places in very small towns where they did not have an ATM where I could get cash using this card.
Also, they charge no foreign transaction fees and actually refund all ATM fees. In addition, their customer service is top notch. I don't know of any other account that offers all of this, especially for free. I met a number of American travelers using this type of account.
I would recommend having a second checking account w/ ATM card that is on the Maestro/Cirrus network (Mastercard) just for emergencies. This came in handy for us once or twice on the road.
Good luck!