XE.com and The Economist are both excellent sources for finding reliable data about exchange rates between countries. Users can calculate the exchange rate between any two countries there.
While either source serves readers well, The Economist offers some additional benefits for its visitors, including allowing users to do standard exchange rate calculations. The Economist has a feature called the Big Mac Index, which tracks the price of the popular hamburger around the world and measures how far it varies from what the price should be given nominal exchange rates between countries. Variations in real prices that differ from the exchange rate suggest there are other economic factors at work.