My strategy is the opposite - take ideas that are often simple to state but whose execution is so complex as to tax the limits of the human mind. Then if I succeed I shouldn't have to worry much about competition (at least for a couple of years).
I often wonder why the software and internet businesses seem so strongly winner take all, where the winner is most typically not the first but the best (in a sense measured by the market) to execute an idea (ie. Microsoft, Google, Facebook). It seems like the classical economic view of competitive markets is becoming more and more of a fantasy world.
"In economics and business, a network effect (also called network externality) is the effect that one user of a good or service has on the value of that product to other people. When network effect is present, the value of a product or service increases as more people use it."
Not just internet and software businesses, railroads, telephone networks, and financial markets are other businesses that are impacted by network effects.
I would argue that Chatroulette has staying power. It's not as popular as it was during the media hoopla, but they still get 250k users day. That's not Facebook or Twitter or Tumblr, but that's enough to get by.
I would also look at Groupon, Woot, and HARO. Simple ideas that have created sustainable businesses.