Are you crawling for this data? Also, since currency is a tricky thing to price (almost any bank/broker can trade currencies) how do you select the "most correct" price?
Yeah, currently collecting from Yahoo! Finance, which has a fairly accurate but hard-to-use API. Advantage that OXR offers is that it's super easy, and responses are about 10x faster and 350x smaller.
Pretty soon it'll be collecting from other services too and taking averages, with a few slightly more complex moving parts, as well as calculations and statistics - that's where we need to beef up the server and start making some dough though.
Also very soon we're starting to collect other types of 'freely available' trade and economics data, and adding value to it in other ways!
Great project btw!