I'm sure a few of these have been mentioned.
Hwy 36 in California from Red Bluff to the coast may be the best motorcycle road in the US.
Though the 2 lane from Hanksville to Hurricane Utah may give it a run for it's money. It goes through so many National and State parks and monuments I lost count.
The Blue Ridge has to be up on anyone list. Try it in the spring when the dogwoods bloom and the tourists aren't around much.
Any of the Alphabet Roads in the driftless area of Southwestern Wisconsin will blow you away. Every county has thousands of miles of paved roads winding through the farms, hills, valleys, coulees and little towns and we owe it all to milk.
Hwy 26 from Copper Harbor to Eagle River Michigan in the Upper Peninsula. Curves and incredible views along Lake Superior shoreline.
"Between two explanations, choose the clearest; between two forms,
the most elementary; between two expressions, the shortest."
Between two motorcycles the simplest (DW)
Eugeni d' Ors (1881-1954); Spanish writer.