I've been reading a lot into the work of sound recordist and gatekeeper of David Lynch sound designer Alan Splet's archive, Ann Kroeber (more to come on her shortly) and came across this handy guide to building a contact mic from kit thats cheaply available at your local Maplin.
A contact mic is attached to a surface, and picks up vibrations and sound created on this surface. So for instance if you were to freeze the mic in a ice cube, you would pick up the cracks and creaks of the ice cube melting; pretty cool eh? Or in Kroeber's use, blend it with a conventional mic to create new and excting recordings which sound like they're from outer space!
Check it out; I shall be indulging in the build and experimentation myself shortly.