Cross-flow fans
 

I found one made by Dynatron - the CF-001. A couple of sites have reviewed this fan and claim it's more quiet than the advertised 38db, and flows about 13 cfm (but both reviewers say it feels like more air than that).

I can't find anyone that sells the damn thing.

It would be perfect for exhaust in a typical ATX case...

------------------------------------ Update ----------------------------------

I found a source, and have two of these little monsters in my hot little hands. They move A LOT of air. If you remove the motor cage, this fan will fit in ATX cases in that little area above the expansion ports (serial, parallel, usb, sound, etc). The fan will also fit in a drive bay.


The source is LZS Global Services - 408-955-0598 - they charge $17 each for the fans.