E-books and information products are well-suited for affiliate marketing beginners in this respect. They are relatively cheap across the board (fifty dollars on average in most niches) so buying a personal copy won’t set you back a lot. You are then in a position to offer an honest opinion on the book, and cater your message to the target audience.
How to Monetize: Affiliate marketing works well when you discuss products on your blog. For our fish tank blog, we would link to all the things you need to buy for an aquarium and then when people click on that link and buy that item (and other items they purchase with it with some exceptions) you get a percentage of the purchase. Amazon Associates is the best-known affiliate marketing program, but there are others like Impact Radius, ShareASale, Commission Junction, ClickBank and Rakuten too.
Although this article has been written in 2007, now in Feb 2014, I still find it full of great advice and tips. What I learned from this article is that when writing a review I should focus on how this product helped me achieve X instead of simply repeating and enforcing the features and benefits of the product that can also be found on the sales page.