Commission Junction: Now, this is an extremely effective way to generate a great income. How it works is simple, you apply for the program, chose a publisher. Then display their ads on your site. It works best if you're advertising something that fits with the theme of your site. So, say your site was based around music, then you'd advertise a music company. That being said, this method works by commission. You are rewarded for each user that signs up for a service or buys a product/item after having clicked on your ads.
Once a user has clicked on your ad, you'll be rewarded with a commission; each commission varies via who you advertise and what the user buys. Now, the beauty of Commission junction is; whoever you advertise, they gives you free banners/text ads for you to display on your site. This makes selling their items extremely easy as well as almost effortless on your behalf. Sadly though, you do not get pay-per-click and users are less inclined to buy a product opposed to clicking on an ad.
ClickBank: This method works exactly the same as Commission Junction, you are rewarded by commission based on what you sell. The only difference between the two is that Commission Junction allows you to basically sell anything. When I mean "anything" I am referring to any product that can be used online, or at home. Whereas, ClickBank only allows you to sell information/digital products (products that can only be used on a computer). Also, unlike Commission Junction, ClickBank does not offer banners to help you sell the product.