Perhaps the best free forex trading strategy I know is the Bladerunner and combined with price action it may just be the easiest to trade.
Update 28 May 2013: the technical basics of this strategy remain unchanged, but I have started using the forex polarity indicator – a combination of the Bollinger mid-band and the 20 EMA – to trade it. There are other minor differences which you will notice if you read the Bladerunner trading blogs, but the essentials are the same: the Bladerunner remains a simple EMA trading strategy. For completeness, I give an example of trading the Bladerunner using the polarity indicator at the end of this article.