I earn very similar to what lemon does ^
I'm building two sites one is education another is a shopping cart im having a strong belief that i can make it successful and am working hard on it.

My tips to earn is that you need to research about different commodities selling online and select a good long tail key phrase
Just aim to get #1 POSITION for that keyword believe me its not so hard(I didnt achieved this for affiliate marketing and am going to do this within a week

) you can achieve that by creating squidoo lenses, hub pages, blogs etc.
And one more important thing is don't tell any one about the product that made you earn good money if you dont want to loose number 1 position by yourself.

Good luck for your future.