Writing copy for websites is another great freelancing option for those who have a way with words. Copywriting can involve writing the text for websites, press releases, promotional offline materials including leaflets and brochures, and any other professional text for businesses. Writing copy can be better paid than blog writing. However, clients can be more fussy, as they want the highest quality writing for the forefront of their website or advertising campaigns. Many freelance writers offer both copywriting and blog writing amongst their services. This can be a good way to juggle regular but lower paid clients (blogging) with the higher paid but ad-hoc project based copy work.
…Marketing an eBook is definitely the hardest part. Ebooks have exploded in popularity and the market is unfortunately saturated with crap from people who thought they could write a quick eBook, put it on an affiliate network, and make millions. However, if you CAN find a good way to market (or possibly have others market by having it listed on affiliate networks) then an eBook can be a great way to make some residual income.
If you have specific writing/journalism skills or are adept in various IT/software domains, freelancing may prove to be a lucrative source of secondary income. Increasingly, companies are implementing a content marketing strategy and turning to outside sources for specific assignments, and if you can prove your worth there will be more work available. Even simple skills like data entry may be to your liking, provide you can offer at least 5-10 hours weekly.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.