Janpanese ZMP introduced the roaming Miuro iPod speaker in September 2006. You can now buy the Miuro internationally via Japanese gadget exporter AudioCubes.
The Miuro has an iPod dock and is actually following you around in the house making sure you always hear the sound track of your life.
You also can control Miuro with a remote to have it roll to a specific place with its 2 wheels (similar to a Segway). You could for instance sneak Miuro next to your sleeping girlfriend/wife and then turn up the volume to max and wake her with her favorite song - she sure will love you for it. The ZMP Miuro measures 350x22mm and weighs 5kg. It can drive around for 3-4hours on a single battery charge. The sound should be pretty good with the 4ch digital power amplifier and multi-channel drive the Miuro comes with. With the Wi-fi connection you can stream music from a PC.
AudioCubes sells the ZMP Miuro for $999, which is about $100 premium to what the Miuro sells for in Japan.