Muffins aside, I think a small laundromat in any college town near the apartment complexes that students live in are interesting.
There was one in my school's town that didn't have any employees (no drop-off service), they just had cameras installed.
They had a waiting room with a couple chairs, bathrooms, about 8 washers and 8 dryers and they charged a premium over what you pay in an urban area. They had it setup so you could pay with your credit card with just a swipe.
Oh, and free detergent on Wednesday.
Not out of control profitable, but I'm sure it's steady, fairly low overhead, and passive as fuck.