To the pure skeptic (KA) I recommend Rene Descartes and David Hume.

You claim I can't prove whether reality is real. You're right. There is no way I can prove that what I sense is an accurate representation of some external reality. I can't prove that I am not dreaming. This is not really relevant, though. Who cares that I can't prove that I am not dreaming. For the sake of argument, lets say that this is a dream. This dream follows a certain set of physical laws; laws which are self-contained, absolute, and can be known through scientific inquiry. This dream world does not require any external deities to make sense. To postulate such a deity would be superfluous.

Now, how does whether or not I am dreaming matter to my knowledge-claims about the laws of the universe in this dream-world? It doesn't. This dream-world is, then, by definition reality, and in reality there are certainly thing which are not possible.

Seeing that we can't actually prove whether or not we are dreaming, is it really relevant to pursue this line of questioning? Are there any applications to the here and now? Of course not. Science deals with the universe as it is now, not with metaphysical skepticism. The assertion that there is a possibility that reality may not be real is certainly not scientific. It is by definition outside the realm of science.

I like science because it works. There are applications to reality. It describes and explains the fundamental nature of reality. Metaphysics can not attempt to do this.