To tell you frankly..No one is going to reveal that thing...Why would an interpreneur reveal how he is tapping the market.You have to research for those...That is what Keyword Research is used for ..
Some keywords will earn good money for one click but nobody is looking for it. Some keywords will earn a few cents for one click but many people are looking for it. So what are you going to choose, think about it.
There are countless threads in the fourm with the same question. I'm sure you can find a good one that will point you in the right direction.
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Buy market samurai or download it and learn how to use it. This tool will tell you which keywords can earn you money once you learn't how to use it. Thanks
It also depends on the source of traffic. Those from US/Europe who click on the google adsense will make more money for you, than those from China.