AMD has opened a new area of their website focused on hosting OpenCL code samples. While right now the offers are a bit spartan (a single Volume Rendering demo), their heart is in the right place. They claim that the demos require the ATI Stream SDK, but the Zipfile offered is source-code and a Visual Studio project so presumably it would work on NVidia systems as well (though you may need to alter a path or two).
Randall Hand
Randall Hand is a computer graphics programmer and news junky that's been working in the field for the last 15 years. He's responsible for visualizations generated on some of the most powerful supercomputers in the world, ytnef, mullion support in ParaView, and VizWorld.com.