Having personally tested almost a dozen different brands i can honestly say that the Panaflo low speed 2000rpm 80mm fan is the quietest of them all.
While slower does = quieter, panaflo have an advantage in that they use fancy self lubricating slieve bearings, which give extreemly quiet operation, while still moving a respectable volume of air.
Most other casefans use ballbearings, which have a buzzy operation even at low speed.
If you cannot find Panaflo fans, you might wish to consider low speed Pabst or Vantec stealths.
I liked the panaflo's so much ive got 4 in my case. 3 x 2000rpm 80mm as casefans, 1 x 3000rpm medium speed for the CPU.
<b>My Computer is so powerful Sauron Desires
it and mortan men covet it, My Precioussssssss!
Regards,
Mr no integrity coward.</b>