An article by Marshall Hall on The PPP theory claims that the AUD is 33% under valued against the U.S. The most overvalued currency is thw Swiss Franc. Its a great read, unfortunately i can only source the first paragraph. However below is a link to an in depth study, as well as a table at the end with all the currencies and their relative values.
"Strewth! Burgernomics might not be a fine art, but it's showing that the Australian dollar is the most undervalued currency among developed economies. That's the finding of the latest Big Mac index, an annual study by The Economist magazine into whether global currencies are correctly priced, based on the theory of purchasing power parity (PPP)."
