I received a Steele cooling vest (with detachable collar) free through the MSAA cooling equipment program. I also got wristbands with frozen inserts that look a little like popsicles. They work really well.

There's also a wheelchair cushion with inserts that you freeze. It's very effective.

--All of these products work well for only a few hours, as others have said. That is a drawback if you're out somewhere and would like to stay cool for longer than that.