Spot forex has always been an alluring asset class to me - high leverage, symmetric short/longs, high liquidity, 24 hour trading ... However, in the back of mind I have always been a bit scared of trading forex to the bucket-shop like nature of the brokers. I think those concerns are less pressing today with the more respectable and regulated brokers (IB, MB Trading, Oanda, ...).
That being said from my analyses, it is hard to come up trading strategies in forex on shorter-time frames that persist which is what tempts most traders. So lately I have been looking at longer-term, daily strategies. Here is one that is both simple and effective over the past two years - mean reversion in the USD/CAD. I like to have a backstory to go along with my strategy and the theory is that the US and Canada have economies that are on similar paths and are married to one another through trade therefore, their currency should not get too far out of whack in normal times. As usual, this relationship would probably break down in a crises (regime switch) so proper risk-management is needed beyond these simple rules.
Here is equity graph from a simple Bollinger Band trading strategy where one goes short at the top band and long the lower band starting in 2010. The parameters are daily 12 MA, 2.2 std deviations, 1 lot per trade (spread of 2 pips) and take profit of 120 pips (a bit optimized). Note that there is no stop-loss in this example. Some results from this strategy: win/loss ratio of 0.84 and max equity drawdown of 28.7%.
One final thing I like about this strategy is that since it is contrarian, you can do the entire strategy using limit orders. If you are using MB Trading, you get paid a small rebate for this which would lower your transaction costs slightly (also MB Trading has "real" limit orders since it is ECN, so you can guarantee that you would get filled at your price or better, which makes this back-test more realistic).