Writing a book can be hours and hours of work but could be a great source of passive income for years and years to come. (ourfinancialpath.com)
Although I don't own any now, if I have other sources of passive income in the future (CDs, bonds, etc.) I'll include them here as well. (themoneycommando.com)
Now there are some special precautions I would recommend when self - publishing a book, but it's still one of the best sources of passive income out there. (toughnickel.com)