Getting paid by the click would be most commonly associated with Google Adsense. This is one of the largest affiliate programs in the world and almost every website has a Google ad on it nowadays.
Why would they do that? The simple answer is that most webmasters know that it is very simple to make money using the Google Adsense affiliate program.
All you really have to do is make the ads appear natural by blending them into a page. Then drive traffic to the page and every time someone clicks on one of these ads you earn a commission.
Google pays out literally billions of dollars in commissions every three months so we know it works. And you have to drive traffic to your website anyway so this is certainly an easy way to make money.
Earning money for leads can be very easy with networks like Max Bounty and others who pay out large sums of money in monthly commissions to website owners.
Up to this point you still have not asked your customer to open up their wallet to pay for anything. You are just asking them to provide a little bit of simple information and click the submit button. Every time they fill out the form that is on your webpage you earn a small commission which can add up over a month's time.
Selling products is the hardest way to make money in an affiliate marketing business, but probably the most profitable if you are representing the right product. One example is to sell an e-book for $40 and earn a $20 commission. If you are targeting the right kind of traffic this can be an easy commission to make.
This is the key to making money selling products online. Before you can start asking or money, you have to have the right kind of traffic coming to your website and then get them in a buying mood.
These three methods can all be easy ways to turn a profit. It ultimately comes down to how you approach it. The easiest affiliate marketing business is the one that you feel the most comfortable promoting and can earn the most money with.