See Currency Exchange Rates in Stocks App on iPhone
The iPhone Stocks app and Stocks Notification Center widget typically is used to follow markets, ETFs, mutual funds, or individual equities, but with the proper syntax you can add just about any globally traded currency to watch as well. Adding currency to the Stocks app should be particularly nice for users who travel often, or anyone who makes purchases with international currency. For some, it may even prove to be the sole reason to use the Stocks app!