Develop a website to purchase and then sell services, such as content articles or purchasing a product at a low price and then reselling it.  Another option is to sell the web design service. Sign a contract with an expert and sell the service to others. This type of business is low-risk and has virtually no start up costs. Sites such as eBay or offer products that can be purchased at a very low cost and then resold to gain a profit.
Rentals, just like stocks, throw off cash. With rentals we call that cash “rent”, and with stocks we call it dividends. A significant difference however is that the S&P 500 has appreciated at ~6% per year (above inflation) for the last 100 years…..Real Estate has had almost 0 growth above inflation. So are rents higher than dividends? Maybe, maybe not. But unless you got one heck of a deal, the delta in rent over dividends will have a very tough time making up for the 6% per year difference in appreciation.
P.S. I also fail to understand your fascination with real estate. Granted we’ve had some impressive spikes along the way, especially with once in a life time bubble we just went through. But over the long term (see Case Shiller real estate chart for last 100 years ) real estate tends to just track inflation. Why would you sacrifice stock market returns for a vehicle that historically hasn’t shown a real return?
A Residual income, also commonly referred to as a passive or recurring income, is an income that continues to be generated after the initial effort has been put in. You can now see why it’s considered to be the most lucrative income source, since it doesn’t require you to trade your time for your money the same way a linear income does. So how’s it possible? Well, it’s another point to team internet. Before the internet, passive or residual income was only possible through a few means whereas nowadays, the possibilities of an earning a residual income is far broader. Let’s review the pro’s and con’s of residual income below:
You can find dividend stocks using Google Finance Stock Screener which is free to use. Set the search criteria for the P/E Ratio, and Dividend yield (shown as a percentage) criteria. You can set minimum and maximum values; in the dividend yield box, set it between 2 and 100. This will search for stocks that pay dividends worth between 2-100% of the current stock price.
Investing in coins and collectibles: Buffalo nickels and Spiderman comic books are good examples of coins and collectibles that can rise in value, and thus offer opportunity for passive income investors. You'll need to get up to speed on the value of any coin or collectible under consideration, but once you do so, you're on the way to price appreciation on a commodity you'll be paying a lower price to buy, and will garner a higher price when you sell.

When I purchase an existing online business, I look for cash flow over the past year and where the money comes from. I want the sources to be more passive so that it does not take a lot of my time. Also, typically I will make an offer that is 18 – 24 months of profit so that I know that I will get my money back within the next two years. I hope that helps!
To create residual income, you need to create something that people will continue to buy on a regular basis long after you’ve created it. A house is a prime example of this as people will continue to pay rent for the right to live in the house. A business needs to have products that are sold over and over again rather than trading the business owner’s time for money.