Any feedback is appreciated! I've spent the last few weekends building a better currency exchange API using node.js and Restify. Other exchange rate providers either charge outrageous prices or only update daily or hourly. MoneyMorpher offers rates updated every minute from a variety of reliable sources. Currently, I have data by the minute for the last 3 years, daily data for the past 30 years, and yearly data for the past 100 years.
One unique feature is that the conversion API endpoint can adjust for inflation over time, so you could convert, for example, 100 EUR on 1/1/2005 to PHP on 5/12/2007.