This semester I've been doing a bit of shader programming (GLSL), and have implemented a series of illustrative techniques for volume rendering. The goal was to simulate some of the techniques used by illustrators and apply them to volumetric data (such as a CT-scan). The first is a CT-dataset rendered using a classic cartoon-shader, it also includes curvature-controlled contours:
Last is a CT-scan of a gecko, using different contour techniques - curvature controlled for the edges, and a low exponent gradient curvature for a bit of shading near the edges.. Looks pretty close to something one might draw on a piece of paper.
Oh, and it's all done in real time.. I love GPUs.. More of my illustravis stuff can be seen at: uib.no