I did a ride up from Phoenix to Denver in about 3 or 4 days that I think was far to fast but amazingly scenic. Go up through Sedona, up Oak Creek Canyon (lots of switchbacks), up to the South Rim of the Grand Canyon overnight. Then, out through the Painted Desert up towards Monument Valley and Four Corners, into Durango for the next overnight. Up the "Million Dollar Road towards Ouray, then over to the Black Canyon of the Gunnison, across Monarch Pass and the Continental Divide, and up to Boulder for the night. Next night was up to Estes Park, across Rocky Mountain National Park (only spot on the trip where I felt the thin air after walking around a field), exiting on the other end of the road, and going down to Colorado Springs to take in Gallery of the G-ds. Continued down to Taos, Santa Fe, and Albuquerque the next night, back across NM and Arizona to Flagstaff (stopping at Painted Desert / Petrified Forest, Winslow, and the Giant Crater), then back down to Phoenix the next day with a stop at Montezuma's castle.
Far too rushed, but the sequence from Sedona to Denver was a real highlight. There's more sites to mix in on the way (Canyon de Chelly, Pike's Peak), and some of these points could really justify a long stay (Grand Canyon for one). I love Santa Fe and Taos.