For some of you interested by demo coding,
there's an image processing library called CImg,
that compiles some interesting demo effects in its sample program
(light bump effect, bouncing bubble, plasma, 3d landscape, fractals,...)
The interesting thing is that this library is multiplateform,
doesn't require DirectX or OpenGL at all, and that it is very simple
Effects programming is very compact (only few lines), it's like a pseudo code when you read the C++ source. Very useful (I think) to learn graphic programming and to create quick effects. This is not especially a demo programming ressource, but it helps for learning on demo-programming.