... more ideas ...

Check this out:

http://www.roadtripusa.com/routes/greatnorthern/greatnorthern.html

That's just one of 11 routes. Woo-hoo! Finally, a starting point for my research. So, let's start:

This is their Drive of the Month for June:

http://www.roadtripusa.com/drive-of-the-month/june.html

The August trip sounds pretty cool:

http://www.roadtripusa.com/drive-of-the-month/august.html

It might be better if I just list the important places to go.

Yellowstone
Carhenge (near Yellowstone)
Grand Teton National Park
Craters of the Moon National Monument
Sun Valley
Flathead Lake
Glacier National Park
The Great Northern (US-2): The UP, Montreal, Lake Champlain
US-20: Niagara Falls and Yellowstone; Finger Lakes and Mohawk Trail

What I really need is a map in which I can put pins. That Google thing is cool, but not really all that helpful.