I assume most people know the matcap trick for using zbrush materials when sculpting. If not, the basic idea is that using a matcap image like this one you can emulate sculpting with the material. You map the image to normal as a GLSL material and make the material shadeless.
Well, because this trick is quite basic in terms of processing power you can also use it to emulate materials at real time. Now obviously a shadeless material would stick out a mile in your lovingly lit GLSL scene but that’s ok. If, in the shaders tab you turn specularity to zero and reflect to full then the shadowing can be quite convincing and you end up getting a lovely material at little cost. Here is an example. Left is unlit, right is lit.
Now, zbrush, the makers of this whole matcap system kindly have a large bundle of these resources freely available from their website. You’re friend Rorkimaru took it out of his schedule to prepare them nice and ready for blender use be it realtime shading or for a nice sculpty render. Now, you should note that while all materials work some will look nicer than others in real time. for instance, something with a lot of texture detail won’t look great if you can move the camera around it but things like metals, plastics, smooth skin and so on look very good.
Here is the file to download: http://www.mediafire.com/?yzqzmgnr22n