Well Guys
Here are a few tips for you.

1- You are not going to be use your ATM, Credit cards, Travel Checks while in Iran. The credit card companies (Visa, Master, AMEX...etc) are not able to operate in Iran.
2- Bring cash. keep em with you all the time. The best currencies to bring are Euro and Dollars.
3- try to bring 100$ bills if you are planning to bring the cash. the smaller bills say $10 or $20 bill would get lower exchange rate when you are changing them.
4- Dont exchange more than 100$ each time. it is going to go a long way till you finish it up. then you go get another bill exchanged.
5- the best place to exchange your money is the Melli, Melat, Sepah or Tejarat banks. these banks are state owned, have even rates and the chance you get ripped off is really lower that street exchange folks hanging outside the banks.
All you need to find a bak is to look around and find the tallest building and i guarantee there is bank either right there or next door!

The exchange rates vary day to day. In Banks they had this big boards that has daily rates on em and you can easily figure out , but if you want to have another source, so you might as well look at the Iran Central bank website at here Exchange Rates

here you can check the exchange rates.

So good luck .