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 adapter 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 $30 iStetho Adapter, 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. [RidRx via The Undercover Scientist, MedGadget and CNET]