Econ 201: The Big Mac Index
After adjusting for exchange rates, the cost of a McDonald's Big Mac sandwich varies tremendously around the world, and weirdly enough, predicts which currencies are likely to appreciate or depreciate.
Big Mac Index - Nice Graphic (The Economist magazine)
Big Max Index - Data (The Economist magazine)
For fun: The definitive discussion on buying hamburgers in Europe. "What did they call the Whopper?"