Our Bonnier-mates over at PopSci.com have a quick totorial about how to make your own X-ray images at home. The process involves suspending something that emits radiation over a piece of high-ISO instant film wrapped in foil. Exposure time varies on how radioactive your source is, of course, but they claim that a shaker-full of sodium-free salt will put out enough radiation to produce an image after a few months.
Check out the PopSci.com page for the full process. Or just try slipping the X-ray operator at the local hospital $50 to let you try and make art with their multi-million dollar machine.