Some places we have enjoyed when crossing North Dakota on I94:
Fort Abraham Lincoln - George Armstrong Custer's last posting before he led the 7th Cavalry to the battle of the Little Bighorn. Several buildings have been reconstructed, including the house he lived in. There is a campground with electric hookups there.
Theodore Roosevelt National Park - The main entrance to the Park is near Medora, but a stop at the Painted Canyon Visitor Center, which you would pass first when heading west, is well worthwhile.
Medora itself is also an interesting stop.
Pompeys Pillar National Monument - is adjacent to I94 in Montana. Captain William Clark of the Lewis and Clark expedition carved his name and date into the stone. Nice visitor center there as well.
If you would like to enter Yellowstone via the east entrance from Cody, take route 212 south from Laurel to route 310 to route 72/120 to Cody. An easy drive.
