I recently purchased a Targus notebook cooling Chill Matâ„¢ and while it does work, it only cools my laptop by 2-5Â°F using the included USB power supply rated at 5V. I happened to have a 6V power pack so I use that instead. When things get really hot I plug in a 19V power pack that I have, it is VERY noisy but much worth it. It works so well that the internal fans shut off even at 100% CPU usage! I'd much rather have my $15 cooler blow up than my laptop.
You could always build something yourself using 120-140mm fans...
That'd be relatively quiet and move MONSTROUS amounts of air to cool the underside of the laptop.