Quote Originally Posted by CyberDruid
I have the same question. How does one make or find counter-rotating fans?
Yes it does...unfortunately there is no way to do this manually. It means buying a fan that spins the 'wrong way,' of which there are only a few (Delta Tri-blade and some sub-mediocre Arctic Cooling models come to mind).

Using a Tri-Blade LE and a Sharkoon 2000 (very evenly matched at ~73.5CFM each) I got tremendous results. However, the Tri-Blade isn't the quietest offering for fans at that speed (though, it's not bad). I haven't done anything more than anecdotal testing of two non-ideal fans, but getting two of the best, even though they spin in the same direction, may end up have comparable air movement at a given dBA level with a radiator separating them.