 <p>The various <a href="http://en.wikipedia.org/wiki/Central_bank" rel="nofollow noreferrer">Central Banks</a>, for example the <a href="http://www.ecb.int/stats/exchange/eurofxref/html/index.en.html" rel="nofollow noreferrer">ECB</a>, provide Forex rates free to the public.</p> <p>There is a <a href="http://pear.php.net/package/Services/ExchangeRates" rel="nofollow noreferrer">PEAR package for Forex Rates</a> and it is also not hard to code it yourself. Since the data is usually updated on a daily basis, you will want to add caching, so as not to hammer the bank's server.</p> <p>However, if your application is doing any time-critical conversion, you should resort to a commercial service, as these usually update more frequently. I think Yahoo and Google have a financial API and someone already mentioned XE.com.</p>