I’ve often found that using litsphere shaders can be useful. They’re cheap and, in certain carefully picked circumstances, can look fantastic. They work by matching there angle of the meshes’s normal to the camera and looking up a corresponding pixel on a lookup texture. Happily for artists this lookup table looks just like a sphere made of the material you’re trying to represent, like so:
I’ve just used a few matcaps from around the internet, none of them were created by me and they are used for demonstration purposes only.
This graph was based on the example given by gestalt.