I was once asking the same question you are. I was searching for some sort of small business that I could enjoy and make money.
For me, A Micro ISV (Independent software vendor), micro meaning ten or less employees, was my answer. I am my companies only employee. I develop software for merchant mariner training and sell it online. It has been much more profitable than my rental properties. The return on investment has been excellent since my total investment in the company was $2000. Compare that to the rentals that required $100,000 in down payments, and we all know how the real estate market has done in the last several years.
I asked several small business owners for advise when I was looking at potential business opportunities. This is my top ten list.
1. Don't have a partner.
2, Try to maintain 100% ownership but always maintain controlling interest.
3. Don't have employees, if possible.
4. Don't start any business that requires a large inventory.
5. Don't borrow large amounts of money (especially from family).
6. Cash flow over growth.
7. Do use a lawyer.
8. Do use a CPA.
9. Find a mentor.
10. Do what you are passionate about.
Good Luck!!!