I took a National Parks trip back in July with a lot of good roads, as well. Around Mt Rushmore was really good, around Yellowstone was pretty top notch, heading into Rocky Mountain NP was great driving through a canyon, leaving Zion NP and heading to Grand Canyon had some wonderful corners, as well.
If anyone plans on a trip around any of those, I can provide a list of the roads I took. I still have the Google Map saved, iirc.
And this is where you find your top speed!