TrueFX has free real-time (multiple updates per second) forex quotes, but only for a limited number of pairs: http://webrates.truefx.com/rates/connect.html?f=html
They also have free downloadable tick data for the same pairs, going back to May 2009: http://truefx.com/?page=downloads
You can get real-time quotes for a larger selection of pairs from FXCM: http://rates.fxcm.com/RatesXML
Realtime rates for about 40 currency pairs are available here: http://1forge.com/forex-data-api, eg: https://1forge.com/forex-quotes/quotes
They also have free downloadable tick-data, going back to 2007, but you need to create a demo account and use a COM based Windows API called Order2Go to retrieve it.
They promised that they will make available the same tick data in CSV format for free sometime this year here: http://www.forexcodesource.com/index.php/Category:Historical_Data