I just opened up a pair of Sonic Impact Flat Fold Speakers and they rock!
Basically the setup is this: you plug your audio source into the amp, a 8 AA battery powered unit and from that amp you plug in the cardboard fold flat speakers. They measure about 19" high by 12" wide and, when flat, about 1.5" deep. Inside them are some transducers that turn the cardboard box into an omnidirectional speaker. It's loud enough to be heard over background noise or traffic (in fact, I'm worried about waking up the people downstairs with how loud I've got them going right now). If you're looking for a portable audio system that doesn't need to plug in and can play for a small group of people, then I'd say this is your product.