Not a comprehensive list (also not in any special order), but it's a start:
Heading west towards Yellowstone out of Cody, WY. Hillside ranches and houses in a wonderful setting. Plus a huge reservoir (named after Buffalo Bill Cody) that one suddenly finds oneself driving along in an otherwise arid setting.
Prior to that, Route 14 from Ranchester (north of Sheridan) through the Bighorn National Forest was outrageous, clearly for me one of the great drives on the trip. Climbing quickly up to 8,000+ feet, the view looking back was maybe the most sweeping of either trip. Very, very memorable. Note: Route 14 splits into two options in the middle of the Forest, both designed as Route 14. We were told that the northern option had grades so steep, one could burn out one's brakes before reaching the bottom. It looks amazing and reminiscent of the Moki Dugway (see below) on Google Maps. I regret somewhat not going that way, but the southern option was gorgeous and goes through Shell Falls, a very neat place with a nice visitors center ... and black noisy clackety grasshoppers. The town of Shell has about 50 people. The next town, according to its sign, has 10 ... but I couldn't find it on Google Maps later.
The Moki Dugway in between the Natural Bridges National Park and Mexican Hat: totally awesome and completely frightening. I posted a video and have written about it more than a few times. Going south, one starts with an 1,100 foot drop with no guardrail, the tightest switchback turns imaginable, dirt and gravel roadway about two cars wide. I truly believe that in the rain, as we were in, 5 mph is too fast to stay on the road in some of the upper switchbacks. Google Map it. Look at the satellite view.
Bear Lake in SE Idaho/NE Utah was a staggering surprise. A mixture of stunning houses and old camps and small houses on the hills and shores was completely unexpected. The steep and twisty road up from there through the Cache National Forest kept the lake in sight for a long time. This is one of the few places, for reasons I still don't understand, where I felt some jealousy for those that lived there or had second homes there. Never heard of it before and in talking with people afterwards at restaurants and motels, most hadn't been there, although a fair number knew something about it.
I'll add to this list later ... I hope.
