Turtledove Kingdom is a program that creates endless random images with no input from the user. The images typically look like softly coloured landscapes - similar yet strangely unique.
The creation process is extensively randomised, so the probability of the same image occurring twice is practically zero - within the lifetime of you and me, anyway.
These images were generated by the software (click to open image in a new window):
Turtledove Kingdom is available as a screensaver (screen effect) for Mac OS X, as well as a standalone image generator application. The screensaver has options for animation, so it's not completely static when it's creating new images.