Currency, banking and money

The official currency in Argentina is the peso. The peso is printed in bills of 2, 5, 10, 20, 50, 100; and in coins of 1, 5, 10, 25, 50 cents and 1 peso.

Banking and money
Buenos Aires' banks are generally open Monday through Friday, from 10 in the morning to 3 in the afternoon. ATMs are everywhere and can be identified by the "Banelco" and "Link" logos. If you have a big bill -- either in American or local money -- you'll find it difficult to get change. You would not expect to get American "small change" in return for your dollars; you would expect "small change" in the local currency. Bus fares are coin-only, and most taxi drivers and small-shop owners will not accept large bills, anything over $20 and sometimes a lot less for a small purchase.
As it is difficult to cash a $100 bill, I suggest you to develop a habit of breaking large bills whenever you can, even if you can pay with smaller bills, so you always have change. If you're stuck with a large bill, look for a supermarket or fast-food restaurant, any of which will usually give you change if you ask nicely. Banks make change, too, but you may have to wait in line.

Credit Cards and traveller cheques
If you use your credit card in Argentina you need to show your (copy) passport .
You will sometimes get a better price in the stores by paying in cash rather the credit card. Ask the price before you buy. Sometimes the price posted will be noted that this is the price for cash.
Maybe your ATM card will get you the better exchange rate and there are ATM's everywhere. You may want to have some dollars or Euros in reserve in case of emergencies.
In Buenos aires, sometimes on holiday weekends, cash machines run out of money. You will have to visit numerous ones until you can find one that has cash.
In some places (also supermarkets like Coto/Norte/Disco) you can buy with US$ or Euros (you better use pesos) and there and many other places with credit card. At supermarket or main shops there are no recharge.
Credit card where you are staying
Some places only accept cash. In areas around Argentina credit cards are not as widely accepted. Make sure and ask where ever you are booking into. Some small towns will not have ATM machines but normally all the major tourist centers/towns will have them.
Traveller cheques are not widely accepted anywhere in Argentina.
American Express: you can cash traveller cheques without any fees at their location in Buenos Aires on the Plaza San Martín area. The address is 770, Arenales Street.