One more thumbs up for Noctua.
I have the Noctua NH-D14 on top of my I7 2600K. It's running at 4.5Gigs for about nine months now with zero isues.
Unless I'm gaming heavilly the processor stays cooler than the motherboard.
Just remember. It's huge! Most solid CPU coolers are. I had to look around for memory that would fit under it. I managed to squize it inside my mid size Antec 900, but you better have good case cooling, because that thing is going to take a lot of space. My older Antec 900 has a lot of good fans and a huge one to the rear top that sucks the hot air out of the case and creates low pressure inside.
I'm very happy with Noctua.