Open Exchange Rates API
Open Exchange Rates is a free, real-time JSON API that provides exchange rates (forex/fx rates) for 150+ currencies, relative to USD.
Rates are collected from several reliable sources and blending together algorithmically, to acheive a consistent and unbiased level of cross-market accuracy.
The latest exchange rates are available on openexchangerates.org, along with historical EOD (end of day) rates going back to January 1999, with HTTPS support, optional JSONP callback and friendly
Access-Control HTTP headers - so you can load it in via AJAX with a cross-domain request without worrying about browser security restrictions.
To get the data, you just need to access
latest.json via AJAX, CURL, Scrapy, node-httpagent, or your method of choice. There's a bunch of documentation and examples/sample projects are coming to this repo very soon.
As with all exchange rate data, accuracy can never be guaranteed when you're not paying through the teeth for the service - and when money changes currencies, everyone takes a cut - so it's a good idea to inform people that these are for informational purposes only, something like "Converted prices/exchange rates are for informational purposes only." Feel free to say that rates come from the Open Exchange Rates service.
Homepage and documentation:
Check out openexchangerates.org for all the info.
This Git repository will soon be updated with working code samples and example projects for using the API and data.