What easily obtained material would work best to protect the LCD screen

We are happy with our Granite. The only drawback is that we have to watch out for stain's - from oil or red liquids like red wine. And even then, as long as you don't let it sit overnight, you are fine, just wipe it up. After living with Corian and Formica, the ability to place very hot pans on the surface it a must. I can't tell you how convenient that is.

depending on the style of granite and edge you use, it may actually be just as cheap as many of the other "cheaper" alternatives. We found that going to the local Granite supplier, was way cheaper than buying it from a kitchen place or major home improvement stores. In our case, we started at Home Depot, and we wanted to see larger samples. They told us to go look at their supplier's location. We went there, and they were like, just buy it from us directly, we not only supply it to Home Depot, but also install it for them, so we completely eliminated the middle man.

Corian is also soft, and can be scratched. They will tell you, "we can fix scratches, and buff it out", but that costs money. Why not just get something that can't scratch.

I am not 100% familiar with all the others listed. I would just recommend going with something that is heat resistant and scratch proof. If any other the other alternatives over granite are also less porous (resistant to stains) that would be a plus.

There is also white board paint, that you can use on a variety of surfaces. Here is one example. You can use this directly on walls, or on a board if you need portability. There is also blackboard paint for use with chalk.