I own a billing company that helps small businesses get their asshole customers to pay up without being jerks about it ourselves. I don't see a dime of the money made off of it, I just own it. My dad operates it in my stead while I'm off to college.
Once I graduate, the business is mine to do with as I please. He plans to be still be running it while I work to get a job of my own, preferably as a history teacher or working in a musuem since writers tend to get their checks few and far between. Or so I've been told to all my friends who've been published. Should I need more money or find work unavailable for some reason, I can always take over the company and start writing my own paychecks.
All in all, it's a pretty good investment. My dad likes it since he mostly oversees it rather than doing the actual work. He's slowly phasing out of his security business and into the less stressful portrait studio business, so even though we're perpetually broke, we're still in pretty good shape.