A fellow ActiveMSer pointed me to this India-based cooling vest company, run by an MIT grad. The vests don't appear to be for sale yet, but wow they look cool. Literally. And very lightweight. If they are affordable, they could change the whole industry. If they work, that is....
http://www.dhamainnovations.com/index.html
http://www.dhamainnovations.com/index.html