I can even name the top scenic drives in the Western US (well in my preference).
For Arizona
Payson, AZ to Globe to Salt River Canyon (beats the Grand Canyon scenery). Then drive from Globe to Tucson (take the back way in the evening), perhaps the most incredible drive in the desert part of the US is from Salt River Canyon down to Tucson. Second best drive is either between Sedona and Flagstaff or on the mountain roads SW of Prescott (I think SW of Prescott is my preference).
For NM
NW of the Silver City NM area towards Arizona is probably the best drive in NM, though the Red River Valley is ok in Fall.
For Colorado
This is really impossible, I would just say starting from near Gunnison to Telluride and Purgatory and then finally to Durango in the FALL if I had to pick one drive in the entire state.
For California
Another tough one, but my favorite drive was most likely on the border of the Oregon and California coast when the elevation starts going back up well over the coastal line (right near the border where they ask if you have any plants that are not allowed in the state). Another awesome drive is from Redding, CA to Medford, OR. Redding, CA is one of my favorite places in the US.
For Oregon
The best drive is probably to Bend, OR from Portland, but you have to go far south first to hit the biggest mountains. After that maybe around Crater Lake (though views are mostly blocked by trees here).
For Washington State
The best drive is in the northern part of the state (HWY 2 and HWY 20, heading east across the mountains), as well as Olympic Park, and also Mt. Rainier (though if I were in an RV, the Olympic Park drive is the easier one)
For Montana
Kalispell to Glacier Park area, Butte is also cool.
Hah, I forgot Texas, my home state...
There really aren't that many "scenic drives" in Texas, there are a few...
For Mountains there are only two really good drives, one being near Guadalupe Peak towards Carlsbad, NM. The other is from Fort Davis to the Observatory, then head north another 20 miles to Sawtooth mountain (the only place in Texas that really has a significant Pine Forest in the mountains).
El Paso is ok, but too dry for my tastes (interesting I suppose).
The coast is nothing special in TX IMO, but Padre island is ok, as well as around Rockport.