Matcaps, no need for lights...

Matcaps, that is what they are called in Zbrush anyway. It is a pretty nifty way to light objects without needing any lights, seems like a useful technique for sculpting.

Thanks to the tutorial at BlenderArtists forum (note: there is a better way to implement this than the first post suggests, just go down a few posts.) and a tip off in the irc channel #smc I spent a day figuring out how to set them up in Blender 2.5, created a small matcap image library.