Need to see everything and ride everywhere. Fantastic country down that way. Watch out for very large critters on the roads through the black hills and keep your camera ready. Be prepared for some cold temps in the high elevations of the Yellowstone area.
Also be prepared for road construction in Wyoming and South Dakota. Their highway departments do a lot of road work during the summer months.
Also, the speed limit in Yellowstone is 25 mph so it takes a long time to get anywhere. And, if you end up riding through the park at night, watch out for animals (wolves, porcupines, deer, elk, etc.) jumping or lumbering out in front of you.
Lots of good riding in the Mt. Rushmore/Keystone/Deadwood areas.