I’ve been testing this Digital Stethoscope by Thinklabs. Unlike most digital stethoscope, this one has an audio out port, which allows you to connect it to a computer or MP3 recording device.
The stethoscope works well — it has a built-in amplifier, and with a bit of practice, you can record heart and lung sound quite easily. It has a noise-reduction feature, which is handy when you are in a noisy environment. It takes two AAA batteries for power. Thinklabs offers some free recording/analysis software for the PC and MAC (based on Audacity). Here is a screenshot of a heartbeat I recorded:
The Digital Stethoscope by Thinklabs is available from Amazon for under $200.