Like writing (above) transcription is another type of work that often equals a full-time income. However, there are lots of sites that accept beginners that don't pay very much for the audio transcribed. While a professional transcriber may not bother with the sites below, someone without the skill to be a professional could use them here and there for some quick extra cash:
Some subjects are much better paid than others, so although you may love the idea of writing about travel (badly paid) a better bet would be a niche like finance (much higher rates of pay). Check out the Pro Blogger job board for high paid freelance writing jobs – other places to look might be Textbroker or you can look at the “gigs” section on Craigslist.
There are loads of resources for making money online as an affiliate. You could source products from ClickBank, Commission Junction, Rakuten Marketing, Share-a-Sale, Impact Radius and many others. Plus, many of the larger companies have their own affiliate programs as well. Do your due diligence and find the right company with a relevant product or service to your audience that you can sell as an affiliate.
For those with a large Twitter following, you can make money from your Tweets alone with Sponsored Tweets. You could be paid for sharing a business’s information, recommending restaurants or hotels, or tweeting pictures of you using or wearing products. As with all sponsored posts on social media, businesses will only be prepared to pay you to Tweet if you have a large following that you can influence. So work hard on building up a loyal fan base.
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.
Matched Betting (not available in the USA) enables you to gamble (nearly) risk-free. I say nearly as there is always room for error! It involves placing bets on all outcomes of an event, using free online bets given out by the Bookies. Although it may take a while to get your head around the concept, Matched Betting can make a substantial addition to your monthly income.
If you’re a skilled worker in a specific niche, like marketing, design, or software development, there are specialty marketplaces that cater just to you. These are amazing places to make money online as you know that the people visiting them are looking specifically for the skills you have. Check out places like 99Designs or Dribbble for designers, Cloudpeeps for marketing and SEO professionals, and TopTal, Crew, or Gigster for high-level software developers. Once you've built up your development skills, you can begin building a brand for yourself as a higher-value consultant and start charging brands for larger projects like implementing an entire WordPress security overhaul or migrating a website from http to https.