What do you have in mind?
Do you want a quiet system or are you exploring passive cooling for the challenge involved?
If you want a quiet system I suspect that most NF4 machines can be cooled while generating minimal noise. I found that the NB47J didn't cool the NF4 sufficiently for my taste so I added a fan to blow air over the NB47J -- a low speed (quiet) fan is enough to drop the temperature about 7C, enough to keep me happy.
Similarly, the AMD cooler for the 939 works well and is normally inaudible if you control the fan speed. Automatic fan speed control is included on most NF4 boards so that part is free, other than the effort of setting up the control.
Of course, at high system loading or overclocking and/or high ambient temperatures the fan speeds increase and become audible.
More about my cooling adventures:
http://www.gadgetbuilder.com/Computer/ComputerCooling.html