I was looking around for a .mp3 player solution for a prop I had an idea for (more on that later), and came across a couple of boards at MDFly.com.
The SD/Thumb drive board behaves just like a regular .mp3 player, but has the advantage of having the controls readily available so you don't have to tear one apart & hack the controls to use it. MP3 files can be stored on either a SD card or a USB thumb drive.
The board that really piqued my interest, however, was the serial TTL interface SD board (sold out as of this writing - sorry). This board is controlled by TTL level serial commands, making it a prime candidate for control by an EFX-Tek controller or a pic or Picaxe microcontroller. The board supports direct play of up to 199 .mp3 files, as well as random playback of a single track.
I have both these boards and can verify that they do work as advertised. Now to use them in a prop... :)