In our zone, potatoes win over corn every time. There is either not enough sun or not enough heat during any given summer to have corn grow well. Sure, it'll grow, but not to its full potential. Potatoes, however, grow in even the worst conditions. Plus, if you eat nothing but potatoes all day (and drink milk) you'll get all your nutritional requirements. They may be starchy, but they've got a little bit of every vitamin and mineral in them.
The next most wonderful vegetable here is beans. They're easy to plant, easy to harvest, and easy to store. I prefer bush beans because pole beans tend to grow taller than me and I don't have fancy trellises for them. If you're practical like me, bush beans are the way to go.
If you have enough space, I want to sing praises for pumpkins as well. Just four pumpkins kept our family in pies for the whole winter (but that's only because I didn't tell my husband how many I'd made, otherwise they would've just lasted a month!). Plus, pumpkin seeds are very high in iron, which is handy for pregnant, nursing, or menstruating women, or for anyone who donates blood regularly.
Although it's not a veggie, I also want to mention rhubarb and raspberries. These perennial fruits are absolutely essential for any northern garden. They require very little care and produce heartily. Oh, and they taste great!
I hope I've given you some ideas about what you should plant in your garden, but you're not limited to this list. I find tomatoes, peppers, and cucumbers (which all love heat) are difficult, but not impossible, to grow here, but you must start them indoors and keep them there until all threat of frost has passed. Good luck!