Affileate programs

There are a number of affiliate programs out there to choose from. I have tried TradeDoubler on one of my sites without and luck.
An affiliate program requires that a user clicks on the ad and then buys something from the company. Otherwise you don't get paid.

With Google ads a click on the ad will generate some money for you.
However, if someone would buy something from the company on the affiliate program ad you will make more money in an instant. Some pay up 30% on how much the user buys for.