Mechanical Turk: Amazon's Mechanical Turk is a resource for doing human-intelligence tasks, or as the site commonly refers to them, HITs. You get paid a very small fee for any given HIT and you'll need a good deal of volume to make a substantial amount of money. But it is a resource you can use in your spare time to generate a small income online.
How much will you make? I think my best month with Google AdSense was almost $5,000 over the last ten years. That amazing month blew my mind since it was actually near the beginning of my blogging journey. When you go from making zero to $5,000 in a month, that will rock your world. For me, it also got me even more excited because I knew there were other ways to monetize.
You can promote your own business or skills on social media, on your own website, on forums, with YouTube videos, and even with super-targeted pay-per-action advertising. What I mean by pay-per-action advertising is, when you advertise on the internet, you can usually target it to a point where you only pay if somebody clicks into your website or even if they make a purchase. As an affiliate marketer, most of my clients only have to pay me if I drive a sale to them. You can leverage that.
eBay is the most popular global auction site around and is a great place to sell items you no longer want. If you are looking to earn some extra cash, start out by looking around your house for things you no longer want; list them on eBay and watch as customers bid on them. You can also purchase clearance sale items and thrift store finds and make a couple dollars profit by listing them as well. The key to selling on eBay is to do your research and find out what the hot items are.