Make/Find something and sell it (food, crafts, art, Ebay)
Provide a service from the home (day care, tax prep, typing)
Write something and publish it (articles, e-books, curricula)
Distribute a product your family already uses, thereby saving money (vitamins, supplies)
Sue Becker, of The Bread Beckers, shares their initial home business vision here; first they became distributors of grain mills and grains, then expanded into teaching seminars for health.
Check your library for The Business of Bliss published by Victoria Magazine, full of artistic photos and descriptions of hobbies-turned-businesses.