Today is Worldwide Pinhole Photography Day: a day where a simple hole and the wave nature of light conspire to create art. I was meaning to construct a simple pinhole camera, but didn't quite get around to it, and today might be too late, but if you are interested, try checking out the forums on f295.org for some awesome information.
I'm killing some time today thinking about how to compute optimal pinhole sizes for specific focal lengths, which leads rather naturally into the possibility of computing zone plates for as well. Note: there are no shortage of formula, none of which really agree, to compute optimal pinhole size, I want to derive them from principle. I'll let you know what I find out.
Above is my sole noteworthy pinhole photograph, taken from a simple cylindrical camera (hence the slightly wacky distortion) onto some kind of Ilford photographic paper, scanned, and inverted in Photoshop. I'll try to put up a picture of the camera later.
Addendum2: Here is the Flickr stream for pinhole photographs.