There are so many great roads out here in Colorado. The roads into and through the mountains just west of the front range all have spectacular views and several are lightly traveled. I have a favorite but I'm not sharing it.
For sheer beauty and even sometimes almost alien landscapes, there isn't much I've seen that can compare to northern Italy and Swizerland in the summer. Alot of the travel is on top of the mountains as opposed to through the valleys that is common here and it makes the scenery quite stunning. Here are a couple of shots of the twisty roads. You don't want to be speeding here, there are unexpected turns, bikers, and police in different places, but honestly, you don't want to speed on these roads anyway.