Here's a rather bizarre passive speaker from Bird Electron. It's basically just a cube with a 3.5mm audio plug sticking out.

Bird Electron announced the "Dice Speaker," a small ampless speaker, and began selling it o­n the same day. It costs 3,000 yen, and is available in black and white colors.

At 45mm high, wide, and deep, it features independent left and right channels. It has a 3.5mm stereo pin jack, and is used by inserting it directly into the audio player. The base has ruber stoppers so that it won't be unsteady when set with an iPod shuffle, Walkman, or other audio player.

Because it has no amplifier, the volume is about the same as a music box, so the company recommends it be used for light background music.

Inspired by:
http://plusd.itmedia.co.jp/lifestyle/articles/0601/17/news078.html

Product Information:
http://www.bird-electron.co.jp/item.html?code=EZ9WB