Digital products such as e-books and brief reports are commonly used quite successfully as tools in viral marketing. How exactly does this work? You offer an e-book or report to your website visitors, free of charge.

This is done by first identifying the niche or group of people you want to market to. Then write (or hire freelance writers to write) an informational product on a topic of interest to the niche group. The best topics to cover would be those that solve a common problem faced by these people in particular.

Somewhere within the e-book or report you can, in a subtle way, mention and affiliate product or website which can help your readers with whatever situation you are writing about. If the content is very useful, some readers may pass it on to others as a good source of information. Even if they don't they may buy something you recommend.

This technique is most effective if your website gives a brief overview of what is to be found in the information product, then provides a form for your site visitors to enter their email address to get the link. This way you can build a mailing list at the same time. The best way to use a list like this is to periodically send a newsletter or other tips related to the topic, while adding a link in your signature or as a P.S. If your list members think you are always selling something they will unsubscribe quickly. If they feel you provide useful information, they will stay with you, and as they come to trust you they will eventually follow one of your recommendations.