-oo-
quietpc.com also makes quiet fans. More air flow does NOT always mean more loud... You can have a small fan spinning at 3000 rpm, an a large (120mm) fan spinnin at 900 rpm olny to find that they both pump the same volume of air and the large is completely un-noticeable.
I have an athlon 1.4 with a 120mm fan spinning at 1000 rpm and you can sleep like a baby during the night with the PC left on if you want to...
Controllers are nice as somebody said. You can tweak the fans during the day, and 'stealth' them during the night...
The noise (in db) depends on the position of the fan also. Be warned, that if you have two fans that make 25db each, you will not get double the noise, nor still 25db. It is a logarithmig scale and you have to make some sums if you want to put everything right...