DEFINITELY the Noctua NH-D14
Tom's has been comparing it with all the those closed loop liquid coolers and only the >$120 ones match it (the ones with the large radiators)
I have it and it's VERY quiet. You can adjust vertically on the heat-sink, how high up you want the fans, so that they fit with your RAM. I ran into stability issues on my 2600K that caused me to keep it OC'ed at 4.6GHz, not thermal issues.
(about how quiet is it? i can hear the HDD writing on low PC loads, and on high PC loads, my GTX 570 turbine fans drown out all other noise the system makes.)