Mindy, Yellowstone NP is a special place, no doubt about that. I have been there a couple of times. Grand Teton NP is just to the south.

South Dakota was on your list as a state, but I am not sure how it figured into your trip planning. The Badlands NP plus the Custer State Park / Wind Cave NP greater area has several scenic drives, sites, etc. A good few days easily! A good AAA map and a couple of travel guides will open up many avenues of adventure.