However, under certain circumstances, payment for personal services performed in the United States is not considered income from sources within the United States. For example, personal services performed by an independent nonresident alien contractor specifically exempted by a tax treaty. For more examples, see the Pay for Personal Service section in Publication 515, Withholding of Tax on Nonresident Aliens and Foreign Entities.
If you are expert in some area, you can always give your consultancy service to smaller businesses who cant hire big companies. When we were brainstorming with a client of ours to generate second line of income, he identified that he has some great knowledge in the area of terrace gardening. He could see that he can help families with large enough terrace to setup their own balcony garden and earn some fees over weekends or extra time.

2) Find Out What You Are Good At. Everybody is good at something, be it investing, playing an instrument, playing a sport, communications, writing, art, dance and so forth. You should also list several things that interest you most. If you can combine your interest plus expertise, you should be able to monetize your skills. A tennis player can teach tennis for $65 an hour. A writer can pen her first novel. A finance buff can invest in stocks. A singer can record his first song. The more interests and skills you have, the higher chance you can create something that can provide passive income down the road.

I knew I didn't want to work 70 hours a week in finance forever. My body was breaking down, and I was constantly stressed. As a result, I started saving every other paycheck and 100% of my bonus since my first year out of college in 1999. By the time 2012 rolled around, I was earning enough passive income (about $78,000) to negotiate a severance and be free.
If you happen to own a home, apartment, or office space, you have a great source for generating passive income at your fingertips. Peer-to-peer property rental site Airbnb has made it extremely easy for real estate owners to make extra money by renting out their homes to guests for short durations. If you're uncomfortable with such a model, you can also use sites like NestAway to find tenants for your property without having to deal with brokers.
This is a buzzword I heard about through a few career coaches. Slowly more awareness is spreading that we can escape the rat race and find alternative ways of working, and indeed, the days of having to choose one particular career path are becoming outdated. The recession is forcing us to think of more imaginative ways to make a living and I am determined to use every skill and talent I have to start generating multiple income streams. Before I was racking my brain for YEARS because I just couldn’t choose one career path! I am only just beginning on a small scale and am not making any real money as yet, but this year I will dig out the toolboxes I’m not currently using and set up various things that will hopefully bring in the pounds. Thumbs up to multiple income streams.
I like the way you have listed the ways to earn extra income and was quite surprise that you did not make mention of network marketing, which is a way to make extra income without quitting your regular, though most people view mlm as a pyramid scheme but the real pyramid scheme is a regular 9 to 5, because you can only have one president of a company at any given time and network marketing business model to promote product that can be used is really cheap to join and can offer a substantial extra income or what do you think?

Has this thought ever struck you mind as what if your boss fired you overnight, what your course of action would be? I guess the answer is NOTHING! You have no monthly pay checks coming in, how are you going to put roof above your family’s head? How are you going to manage the bills payment? What would you feed to your family? An answer to all this lies in darkness…complete darkness in that situation. But I have answer to this question, because I am my own boss managing multiple things and earning from all of them at a time, losing one would not be that big deal to me.
Build a list in a particular niche and tell them stories. Create a bond. Build a relationship with them. It's important. Then, when you've created a bit of culture, start marketing affiliate products or services to them that you think they might like. Just be sure that you personally vet out whatever it is that you're selling to avoid complaints if the product or service falls short.

Stocks (shares) paying dividends are typically a reliable source of income but they have higher risk of capital losses than cash and bonds. So, it’s wise not to chase yield indiscriminately.  The 10 highest yielding stocks on the ASX 200 (the 200 largest companies in Australia) are shown in the table below.  But their share price performance on average over the last year has been underwhelming, as shown in the far right column: