http://www.newscientist.com/hottopics/t ... technology
A quote from the article:
Sounds promising, adding these fans to existing fans, meaning you could run existing fans slower (if they're not already at 5v).When Garimella put a piezoelectric fan inside a laptop computer with a rotational fan, it brought the temperature down by 8°C. The piezoelectric fans are far less power hungry, he says, using about one per cent of the power needed by rotational fans
Also - they don't make any noise!
Although I don't think any such devices are going to be available any time soon.