One last method I want to mention briefly is offering a service online. A service can be anything you can do for someone. For me, it was writing articles and providing content.
If you are good at something like web design, programming, and writing to name a few, you can make money online without an investment on your part.
All you need is a place to reach people looking for your services. Freelance websites and webmaster forums are a great place to start. You can even head over to Fiverr and offer your services there.
You can sign up to most of them for free and market your services. Just make sure you abide by the rules. If you need some quick references, I would check out Odesk, ELance, Digital Point Forum, WickedFire (Forum), and Fiverr.
The following post goes into more detail about offering services online to make money: How to Earn Money Offering Your Skills Services Online
