vegas:

mt charleston is incredible. goes from red rock southwestern desert to alpine forest in like 17 miles
red rock is my favorite loop and definitely worth paying imo
round mountain loop is an old HWY that they converted into an MUP. its incredible.
the road from lake mead out to valley of fire (northshore road http://goo.gl/maps/HCs3I) is absolutely pristine, beautiful pavement and you can easily go an hour without seeing a car or a living human being, and valley of fire itself is pretty stunning and great terrain.