Moshi's Zefyr is a portable cooling pad for the MacBook that provides a near silent fan, powered by USB, and offers a temperature drop of roughly 3 degrees Celcius. The Zefyr is designed to place your MacBook at an ergonomically beneficial tilt, and when not in use, the Zefyr collapses to better fit in a bag.
The Zefyr also provides a pass through USB port, so that peripheral use is not sacrificed. A portable cooling pad might be a little silly, but for anyone who's experience the heat of a MacBook on their lap, and worries about going sterile, it may be useful. It's available now in black and silver colours, and sells for US$75. [Moshi]