While I was in New Zealand, a friend had a little bluetooth speaker the size of a lunch box.
It had two 3" speakers and was VERY loud with clear bass. It apparently cost $60NZD but I forgot to ask what brand it was.
If I ever find out, I'll post it, as I was seriously impressed by this thing. It came with a built in rechargeable battery that plugged in via a PS3 cable (USB B?) and lasted something like 6 hours