Did you buy something in US$ with your credit card, but your credit card only reports the total in Canadian Dollars, so you don't know what they charged you, or what their commission was?

Here is the daily US Dollar to Canadian Dollar Exchange Rates, noon-time rates. Data is from business days only. Generally, changes are minor on holidays and weekends (though it is true that the forex market is open 24/7 and rates are constantly fluctuating). 

Looking to make a trip to the USA?

Travel (cheaper) internationally from the US? Flights there are usually a lot cheaper than in Canada. 

Buy a car in the US?

Going to University/College in the USA? Or need UK Pounds to g o to school in England?

Buy a vacation home in Florida? US Stocks?

For all of these things, you'll need US Dollars/American dollars to make the purchases.

These are the Canadian Dollar to US Dollar Exchange rates (noon time), day by day for July 2009.

The source of this data is the Bank of Canada (equivalent to the US Federal Reserve Bank).

The average rate, highest rate and lowest rate for the month of July 2009 are at the bottom of the page. 

You can use these rates to compare to the rate your credit card offers or other foreign currency transactions.