A great webpage containing several noise circuits can be found here. http://www.ciphersbyritter.com/NOISE/NOISRC.HTM
How useful are noise circuits anyways? Well for one, if combined with an Envelope circuit they can produce sounds similar to HiHats, Crash Cymbals, and Snares. Also quite interesting if patched to a VCO creating a sort of random/chaotic tone generator. At any rate, cool page with lots of images, sound files, and schematics.