Kristin,
Have you looked online for a list of native plants for your state? These wouldn't need as much care as plants not normally grown in your area. I would suggest:
Rudbeckia hirta (Black eyed susan) In my garden it can be a little aggressive, but you can deadhead it so the seeds don't spread. The Echinaceas (Coneflowers)are wonderful and there are so many colors now. If you are able to cut them off in the winter or fall, native grasses add another layer of interest to the garden and they come in different colors and sizes! I have red grasses, blue, chartruese, deep green and striped! The Becky Shasta Daisies are very reliable and beautiful. Liatris (purple or white) will attract the butterflies, as will Culver's Root and Joe Pye Weed. Hope this incomplete list gets you started!

Kristin,

What bev2009 said regarding Rudbeckia, Echinaceas, and Shasta Daisies. Two self-seeders that also do well here in Zone 5 (Kansas) are Knautia macedonia and Bee's Balm (Mondarda sp). I've got a couple of vast masses of both self-seeded. I also find some columbines self-seed regularly in my area.

Here is a link that might be useful: Garden Musings

Whoops; can't spell; it's Monarda sp for the bees balm.

This is an old post, but I have Bee Balm & find that it is very invasive. It's a member of the mint family. It spreads underground & is very hard to control. It has it's place, but not in a flowerbed where you want a variety of flowers.