The best examples are probably in diet, e.g. Weight Watchers, and Jenny Craig. There's a huge industry around drug & alcohol rehab, though it's not easy to see which parts could support startup-type scale. A bunch of these needs are served in the healthcare industry, often with much room for improvement. Healthcare is a totally massive industry.

It's not an easy place to build a business, but there are lots of resources spent on these problems now. They affect families, businesses, and individuals. Figuring out how to line up these things and make a viable business is complex, but some people will figure it out.