Free Currency Converter... And Then Some!
Before moving on to the subject let me give you a little bonus. Those of you who are really into Google probably know it already but some of you may have no idea how easy can one convert currency simply by using Google Search and nothing more. You don't have to Google for "currency converter" simply type in for example "100 USD to EUR" and type Enter that's all! Now let's take things even higher...
... and take a closer look at OANDA. I never heard of it until today so I can't exactly tell you how popular it is (sure I can check its traffic and PR but popularity isn't always about the raw numbers). Popular or not this one's surely one useful online service since it offers currency conversion for about 170 currencies with daily and historical rates not to mention its multilanguage support and custom rates (basic interbank +/- rates)!
If you're a webmaster then you should be happy to know that OANDA also offers a currency converter widget for your website not to mention the free iPhone currency converter tool currently able to work with 180 currencies and four metals (heavy metal maybe? or at least thrash metal? haha!). Pretty cool tool if you ask me...