True what you say _bob, someone somewhere has already fond, used and improved every strategy any of us could think of.
The converse must therefore also be true - the successful strategies are pout there and everyone who has read and tried enough strategies must have run through at least one winner, just maybe without realising it. Statistically the oldest strategies have the best chance of being amongst the winners - if they were obviously almost always losers, how could they have not become extinct?
I'm a fan of trend-following - find the trend, buy on the pull-back, ride it till it dies.
But I also kind of want to believe that price crossing a MA can work. Its been around so long it just must!