The Sri Lankan currency is the rupee (Rs), which is divided into 100 cents; pricing in cents is rare. Rupee coins come in denominations of one, two, five and 10 rupees. Notes come in denominations of 10, 20, 50, 100, 200, 500, 1000, 2000 and 5000 rupees.
Credit Cards are widely used and accepted by local establishments (even in small towns). The most widely used card types are Visa and MasterCard, with Amex to a lesser extent. It would be a convenient option to use your Credit Card (valid for international use) whenever possible.
US dollar approximate rate is USD$1 = Rs152
Euro approximate rate is €1 = Rs166
ATMs are easily found in towns and cities of any size. ATMs often issue Rs 5000 notes. Try to break a few as soon as possible as small vendors may not accept large notes: you can usually do this inside the bank that operates the ATM.
Any bank or exchange bureau will change major currencies in cash, including US dollars, euros and British pounds. Change rupees back into hard currency at the airport (before security, there are no exchange counters after) prior to leaving, as even nearby countries may not exchange Sri Lankan currency.