Fixer.io - Fixer provides a free, simple, and lightweight API for current and historical foreign exchange rates and currency conversion. The API tracks rates published daily by the European Central Bank.
WorldData.ai - Analyze and download over 3.3 Billion curated external trends.
exchangeratesapi.io - Foreign exchange rates API with currency conversion.
data.world - The social network for data people
xChangeApi - Easy to use, free live updated foreign exchange rates API
Quandl - Financial Data API - Financial Services