Prostitution, food, housing, alcohol, cigarettes, construction, car maintenance, used car sales (buy them at auction and bring them in), illegal drugs (there is probably a certain predictable dollar flow per capita anywhere in the US, varying by "class.").
Just look at everything you see around you every day and don't really see; there are probably huge pockets of under-served markets for "everything."
The operator of a coffee kiosk on the right crossroads would probably be exhausted.
Most business opportunities there are currently severely constrained by an insufficient supply of labor and housing. Fast food jobs pay $15/hr. I've heard Menard's (a Home Depot-like chain in the midwest) flys people in from Texas for a week at a time to work at their retail stores because they can't find any local help.
I live in Minot, ND, and previously worked at the Menards here in town.
Right now, they're flying people in from parts of Michigan, and I believe there are others that are being flown in from a store in Minnesota that's currently being rebuilt.
A Taco Johns here in town is starting people at $13/hr. McDonalds is at $10/hr and a $500+ hiring bonus. One of our nicer Italian restaurants in town just closed down as they couldn't find enough people to work. Kohls just built in town (the building has been done since November), but they won't open up until mid-March, as they still haven't found enough workers.
There's a lot of potential for businesses here, but the lack of workers and reasonably priced housing really hurts. The housing isn't hurting only because of the influx of oil workers. It's hurting worse since the largest city close to the oil had 1/3 of it flooded in June of 2011. Not everyone has rebuilt.
In the east, there's a ton of tech. Microsoft's second largest campus is in Fargo, and with that comes a lot of satellite companies (vendors, consultancies, etc). There's also nano tech and a ton of biotech here. UND in Grand Forks is well-regarded in the region for its aerospace program, and there are plenty of opportunities in that field. In the last 20 years or so ND has gone from largely agriculture-based to fairly well-diversified between ag, tech and natural resources.
If you're thinking of moving here, though, let me tell you that anything anyone tells you about the winter is truly unimaginable. You need to actually experience -30 degrees to understand it.
