Sony NW-S23 256 MB Network Walkman

Features

Powered by 1 AAA battery for up to 70 hours of use; connects via USB 2.0
256 MB of flash memory; holds 4 hours of MP3 and 8 hours of WMA files (CD quality)
Sport-oriented player weighs 2 ounces and measures less than four inches long
Armband-style carry case
Compatible with content from Sony Connect Music Store

Product Description from Sony:

The Sony NW-S23 is water resistant, provides up to 70 hours of playback on one AAA battery, features a skip-proof design, and comes with an armband strap for added convenience. The unit is small, weighing in at 2 ounces and measuring less than four inches long, and its high-impact plastic housing is designed to take a beating. If you want a digital music player that's tough and tiny, get the NW-S23 S2 Sports Network Walkman. It won't get in the way of your work-out.