It doesn't have the most appealing design, but the Sherwood Digital Audio Card does happen to be the world's thinnest MP3 player at only 5mm thick. Weighing just 48g, this credit card sized player sports a 2-digit display and interchangeable faceplates. It gets up to 8 hours of continuous use when the Li-Polymer battery is fully charged.
Source: [TheMP3Players via GadgetReview]
