Assuming you follow -80 to 90:
Some Good places to stop - In Indiana off of I-80 is the Indiana Dunes area. The KOA in that area was pretty nice for an overnight.
The Dells area of Wisconsin all have nice campgrounds, but can be full depending on the time of year you go.
South Dakota - Mitchell - Stop there and see the Corn Palace, it's different every year, the KOA there is OK, good for an overnight.
One place to avoid if you can for fuel is Exit 170 (1880 Town) on I-90 in SD. Pricier fuel and not that good of a fuel stop - the campground just down the road on Exit 170 on the other hand is real nice with a small mom/pop restaurant.
If you have the extra time, and don't mind the route, cut north through Canada to Sault Ste Marie and cut through upper Michigan through Wisconsin down to 90. It's about 300 miles further, but enjoyable drive.