"Fire up a bakery or production kitchen
Do you have an unused mother-in-law apartment or an industrial-size kitchen that sits vacant all day? Rent it out as a food production facility.
“Food-oriented businesses tend to be very successful.”
Custom cookies and cupcakes, delivered gourmet meals and birthday-party catering are popular services that don't require a storefront but may need additional ovens and kitchen space.
"Food-oriented businesses tend to be very successful," Jones says.
Share your garage
If you have a garage you never use -- or an extra spot in a three-car garage -- consider renting out that unused space.
A weekend mechanic who lives in an apartment may pay for the chance to work on his or her ride in your garage. Others may be looking to store a motorcycle, boat, trailer or recreational vehicle.
Still others may prefer the location or convenience of your garage to the local self-storage options, especially if the price is right. If your home is out in the country, you might even discover the next U2 by renting your garage to a local rock band.
Grow your own money
If you've got a green thumb and a bit of tillable land, consider growing a cash crop.
Although commodities, such as wheat and cattle, are well beyond the scope of most backyards, berries, flower bulbs, vegetables, grapes, florist products and landscape plants can be cultivated and sold to wholesalers, at farmer's markets or on your front porch.
In the Northeast, you can even tap your maple trees and sell the sap to a sugaring operation.
If you didn't get the green-thumb gene, take a slightly different approach.
For example, enterprising Princeton classmates Tom Szaky and Jon Beyer started their own worm gin, which produces a potent organic fertilizer from worm waste.
Their company, TerraCycle, now sells its products to Home Depot and Wal-Mart. Although Szaky and Beyer started their worm gin in the basement of an office building, you could start a similar venture from the comfort of your home."