Currency Converter HD is available for free January 15 & 16. This popular app claims to be the most powerful currency converter in the App Store. It covers over 150 currencies and offers real-time currency conversion with up-to-the-minute exchange rates. The app has three different views: calculator, chart and list view. It also has an offline mode using saved rates, so that you can find the exchange rate when traveling abroad even if you don't have an Internet connection. You can see a demo video here.