1. Offer Your Services to Your Neighbors
Even the least skilled person can offer services that are valuable to someone else. Are you a handyman? Do you own a lawnmower? Can you babysit? Any of these skills can bring income, and there's no better way to start than telling your neighbors that you are available for hire. If you do a good job, bringing extra cash home might just become a regular event!
2. Rent Out Your Room
Whether you rent out one of your rooms for the long term or by the night, I'm sure you will welcome the income that it brings in every time someone writes you a check. With services like Airbnb.com, doing so is much easier than you think. List your property, and start enjoying the extra money that your space can generate! (See also: 7 Steps to Market Your Extra Space as a Vacation Rental)
3. Take Out a Mortgage, and Invest the Rest
This isn't for the faint of heart, but with the favorable tax treatment of equities, the returns of a well diversified and tax efficient portfolio will have an extremely high probability of outpacing the interest you are paying for a mortgage, especially after you consider the tax consequences.
I caution you though that this is only for people who can tolerate short term volatility. For most people, I recommend paying off your mortgage early, let alone taking out a bigger mortgage than necessary. If you choose to go this route, you absolutely have to stay on track with your investments even if you might seem like a fool in the short term, so think carefully before you take this advice.
4. Line Up
You can sell your own stuff on eBay, but eventually, you'd run out of everything! However, if you are able to get in line on all those hot gadget releases and be one of the first few to purchase one before it's sold out, you can almost guarantee yourself a tidy profit. All you have to do is line up ahead of time and buy the product, and when it is out of stock, you put it up for sale at a higher price than you paid for it.
Don't get greedy though, because if the product happened to become readily available, you might have to sell what you lined up for at a lost.
5. Start a No/Low Cost Business
Remember all those services you offered to your neighbor? You can probably turn that into a side business without putting up a ton of capital once you figure out that your expertise are in demand. You can start out of your home and grow from there. Who knows? It might turn into a multimillion business one day, which could transform your finances!