If I have a blog that is getting 100,000 page views a month that means that I’m probably getting at least 50,000 people to the site (most blogs will do between 1.2 to 1.4 pages per session). That means I have to try and get some small percentage of those people to buy something from me if I really want to do well. If I can’t get them to buy something then (in some cases) I have ads running on the site that will make me money anyways.
– Project Payday is one of those sites that has testimonials of people who have earned thousands of dollars by getting paid to get trial offers. I’m not saying you’ll earn thousands, but it is legit and you can earn some extra cash. They assume that by paying you to do a free trial, you’ll either like the product and purchase it, or forget to cancel the trial and get charged for it. If you can keep track and cancel before you get charged (if you don’t want the product), then this is a great site for making some money.
Affiliate marketing is a tricky business. It involves years of training and understanding of things like consumer psychology, writing compelling sales copy, understanding search engine optimization and online marketing, knowing how to build sales funnels and squeeze pages and so much more. But it's also incredibly lucrative. Some affiliate marketers make millions of dollars per month, but reaching this level is excruciatingly hard.

The peer-to-peer concept is coming to virtually every corner of human existence. That includes the hospitality industry. Through AirBnB you can actually rent out your house for various lengths of time for a predetermined fee. That gives you an extra income on your house and gives the visitor the benefit of having an entire house, rather than being crammed into a single hotel room.

Audiobooks are another lucrative form of passive income. Speaking from experience, when done right, audiobooks can easily produce thousands upon thousands of dollars per month on autopilot. However, quality and the delivery of high-value content must be the key aim at all times. Leverage Amazon's ACX platform to publish audiobooks for inclusion in Apple's audiobook store and on Audible.com.

But don't make the mistake of thinking this will be a passive source of income—you're on call whenever you have a guest and you'll always need to keep the place clean for incoming visitors. On top of just renting on Airbnb, consider offering your guests paid add-ons, like Lauren Gheysens', Royal Day Out in London, England—where she gives visitors a local's only tour of the city, complete with bespoke 18th century costumes.
If you really wanted to make the list even more exhaustive, you could also discuss the various biological money-making methods (e.g., sperm donation, egg donation, etc.) and/or go into the more technical (e.g., hosting websites on one’s own server, building computers for others, etc.). Also, you could potentially explore those well-known money-making ventures, such as trading on the stock market, which are seemingly difficult to enter into by their apparent complexity by listing various online instructional tools which assist novices looking to get involved in them (e.g., Investopedia’s online simulator to prepare for buying/selling stocks). Sometimes those methods of making money which appear to be the most difficult are, in fact, relatively simple once you understand the underlying conceptual framework – many people just don’t realize this.

If you have a flair for designing cool images, don't bother about creating your own inventory. As long as your design can be printed on a product, you can pocket some money. You can upload designs on various Websites such as CafePress, and if somebody orders these designs, the company will print them and distribute the products. It could be designs for T-shirts, hats, bags, books, posters, calendars, greeting cards, etc. You will receive a commission for each sale. Other such sites include Lulu and Zazzle.
Robo-advisors are diversified investment accounts that are automatically managed by a computer algorithm (as opposed to a human money manager). If you want to invest, but don’t have the money, or don’t want to invest with a money manager, robo-advisors are for you! Robo-advisors make investing easier—and cheaper—so they’re perfect for new investors.