Ppls here say Noctua NH-D14, Prolimatech SuperMega or Megahalems, or Thermalright Venomous X is best air cooling. I have heard that at high OC the NH-D14 is superior. If I had known this, I would have got it instead of my Mega. However, there is only little difference.

But whatever you get, make sure your case is roomy enough for it, and make sure you memory is not too tall to interfere with it.

Here is a review that gives quite a bit of info on the Prolimatech Megahalems, I think it was before the "rev. B", and it now includes clips for two fans.
http://pcper.com/article...aid=771&type=expert
 
The Supermega is just a Megahalems with some copper fins, and gets slightly better performance.