http://www.mikeash.com/?page=software/gpulife/index.html A MacOS X screensaver which runs the game of live in a OpenGL shader, which means that the entire screen is being drawn by the graphics card. You can use this as a sort of benchmark for Mac graphics cards.
http://www.spikedhumor.com/articles/19017/Pacman_Running_Around_Library.html Pacman takes a trip to the library.
http://alan-parekh.com/projects/hard-drive-clock/ A guy makes a clock out of a hard drive by using LEDs to shine a beam across the platter with different colors of light for hour, minute, and second hands.