BEAST Currency Converter

As its name says, it's simply the BEST currency converter out there.
Besides being super easy to configure (no coding needed), it's the multi-currency app that has the most features using a very intuitive interface.

A sweet bonus is the ability to see your product prices in the original currency of your store as well just by hovering the mouse over them and the stellar support from the developer - quick response time is definitely a plus for me.

Oh, and it really looks great on the mobile version of your store!