When travelling to a foreign country, it is advisable to carry a variety of forms of payments. It is important to have some cash in US Dollars and local currency as well as credit or debit cards. Visa cards are accepted in most places, however, American Express, Discover and Master Card can be unacceptable in some places. The advice is to have several sources of money in case one fails (ATM eats the card, lost cash, etc.).
The exchange rate of US Dollar vs other currencies is constantly changing. Please visit XE at http://www.xe.com/ucc/ to get current values.