It's only intended for recreational use, but this feels like another step towards a real-life tricorder. A new start-up called RidRx is selling an adaptor that connects stethoscopes to the iPhone/iPod touch and uses their app for fancy spectral imaging.
You'll need to attack your old stethoscope with a pair of scissors to make it fit the $US30 iStetho adaptor, but they'll provide full instructions. Once connected, the iStethoscope Pro app (iTunes link) "amplifies the signal and eliminates audio outside of what is important for diagnosis". Kinda crazy.