Here is a device that basically explains itself. The Retro Cube Mini Speaker with MP3 Player is from fu-bi of Japan which features a 3W x 2 channel speakers that should render some great tunes from various sources. You can hook it up via USB 2.0 connection or directly from a SD/SDHC memory card since the speakers come with a built-in MP3 playback capability. The battery is good for 3 hours of use. This is now available in Japan for $50 but no word on whether it will become available internationally.

(Source) Ubergizmo