iLuv is offering the ISP150 Bar Speaker, which will turn your iPad into a music box. It will work with the iPad, notebook and iPod. The integrated speakers can be powered by either USB or four AAA batteries.
Some other features include a 3.5mm audio jack, USB connectivity, a power switch and volume control. It will cost you $34.99. Judging by the image it doesn’t look all that portable. It doesn’t seem like something you want to be carrying with your iPad.