The awesomely geeky iPod Lego-brick speaker block that we first saw all the way back in 2007 has made it over to the US and UK, and is finally on sale. Known as the iPod Brick, the stereo speakers click into the dock connector and the middle two bottom pegs work as volume buttons.
The iPod Brick is compatible with the 3rd, 4th and 5th generation iPods, 1st, 2nd and 3rd generation iPod nanos and the iPod touch, but somewhat bizarrely not compatible with actual Lego. They don't have their own battery, so they'll leech power from your PMP, but given the tiny size of the speakers I can't see it making a massive dent in your overall usage time.
There's even an "Active Bass System" which promises to improve sound quality, though how much mileage you'll get remains to be seen. Still, a neat little stocking filler and available both in the US, for $19.99 (though seemingly only in blue), and in the UK, for £12.99 (in red, white and black).