Music may perform better than books and other products, mainly because you can listen to the clips of an entire album in roughly 10 minutes and get a good enough feel for it without buying it to write a short review. If you have another topic that you're passionate about, great, but make sure you have a unique angle on the topic. People can get reviews about a lot of those consumer products anywhere. You need to give them a reason to visit your site.
If you have a propensity for writing and you can slay with your prose, consider writing an ebook. While the market has certainly become saturated as of late, books that help teach people about a technical topic still sell extremely well. This is a great source of passive income but does require a large amount of effort at the outset before any money is generated.
If you design a wildly popular app (which is harder than it sounds), you might be pleasantly surprised with the income they generate. Offering one or more apps at the iTunes or Android app store gives your creations wide exposure to prospects. And income can be generated by charging for the app, displaying in-app ads, or charging for in-app features and upgrades.
Building trust with your audience is paramount in affiliate marketing, and the quickest way to lose trust is to recommend products either you haven’t used before or that aren’t a good fit for your audience. Also make sure you never tell anyone to directly buy a product, you are simply recommending the product. The more helpful you are and the more you make quality recommendations, the more likely your web visitors will come back for your expertise. 
Yesterday I earned $506.03 from Amazon. It was actually a pretty good day, higher than average. One might think the higher than normal figure came from selling some big ticket items but that wasn’t the case. The highest commission for the day was a $21.34 commission. The vast majority of the sales were books sold from my list of photography books, which we promoted on social media recently.
It's especially true now that the big media players are finally waking up to affiliate marketing (NYTime buying WireCutter and SweetHome) and BestReviews (which was already an epic product review site in it's self due to the fact they built their own 10,000 sq ft testing lab) being acquired by Tronc (owns the LA Times and half a dozen more publications).

27. Sponsored/paid posts – Many blogs publish sponsored and paid posts. Sponsored posts are basically just posts about a specific brand, product or service. A company will pay you to publish an article about it. It’s similar with other paid posts as well. Your basically selling the spot for the article on your site. If you decide to take this route, you’ll want to build your traffic before you will get many offers.
I have a free WordPress website with 1000-2000 visitors/month. I was trying to place Amazon Affiliate ad links last night and failed/flailed mightily. I would paste the links into my posts in the HTML mode, switch to Visual mode, and could see the image. However, every time I tried to save or update the post, the image reverted to the gangly hyperlink. As some suggested, I tried cleaning the links of any formatting from the copy and paste with text edit. No dice.
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