There are 1000's of affiliate programs you can find around the net. But not all of them would help you to earn money online. Some affiliate networks pay more and some affilaite networks pay less. You have to choose the best one for your site. Its not just which affiliate program pay more. you have to check which affiliate program suites your niche and which will give yo more sales. for example Amazon affiliate program is infamous for their low commision rates. But for sites about books they are best affiliate program you can find.
To earn from Affiliate programs you need lot more traffic than for PPC ads. Also Traffic has to be better quality. You earn only if the user buy something or complete something seller want. There are various types of Affiliate programs such as CPA (cost per action) , CPL (cost per lead) , Cost per download etc.