Here's some links to ND and MN scenic byways
About North Dakota's Scenic Byways and Backways (http://www.parkrec.nd.gov/byways/index.html - broken link)
Best Scenic Drives in Minnesota | Best Scenic Drives Minnesota
In the summer, I think Highways 18 and 32 North from the Larimore area are very scenic in their own way - as they give some "vistas" looking down on the Red River Valley. They also lead to Icelandic State Park near Walhalla, and the Pembina River Gorge. The Walhalla make be a decent place to check out anytime. As you go north in the valley, the ridge separating the valley and the drift prairie (pot hot region) becomes steeper.
Following the Sheyenne River from south of Devils Lake can be a picturesque drive - but again especially in the summer or early fall.
Further west in ND, there are a number of scenic drives - none of them very well traveled.
http://www.dot.nd.gov/imgs/nd-highway-sys-lrg.png