Really depends on your "quietness" threshold... All I mean by that is how quiet do you want it to be? Bigger fans are quieter, but they may be difficult to orient in the case so that they blow over the heatsink (i.e. you may have to make creative use of some tie wraps and screws to get the fan where you want it.) Also, spending a lot of time choosing the quietest fan might not make sense if its installed beside a 7800GTX and its 58 (or so) decibels of noise... If your other comonents are all real quiet, a Nexus or Yate Loon 120 would satisfy most.
Personally, I use a Nexus Silent 120 in most of my cases - mainly because I can't hear it, and because its fairly available to me...I could never easily find Yate Loon and Panaflow fans. The Nexus doesn't move alot of air, but for the NB47J, it doesn't really have to, in order to keep temps down. Silentpcreview has some good reviews on a variety of fans, and is worth checking out.
Cheers,
A
PS. I'd re-consider Operandi's suggestion as well, since I think that the "inverted heatpipe issues" are non-sense. Gravity (hence orientation) should have nothing to do with the operation of a heat-pipe, and its internal wicking mechanisms. Of course, if you've found info that shows people having ACTUAL problems caused by inverted heat pipes, I'd love to read it!