From Star Trek IV, transparent aluminum. We already have this, but we call it sapphire. WE use it as the lenses of missiles that are laser guided. The sapphire is coloered red, so it would then be a ruby, but it can withstand desert sand at 600 mph, and not get a scratch.
We also use it in the manufacture of circuit boards, as it is also radiatoin resistant, good for use in space.
I just think we haven't gotten down the price of manufacturing enough to mass market large applications to the point where it is competitive with lexan and the like.