18~27.5dBa is pretty quiet.
The 120mm model is 20~32, still quiet.
I prefer the ZALMAN CNPS9500:
Silent Mode 18.0dB Â± 10% Low-noise Mode 27.5dB Â± 10%
Here's a quote from a customer review:
simply marvelous fan! didn't have the concave base issue as some unfortunate reviewers have had, but i upgraded to this from a zalman cnps7000-cu led which was already quiet enough, but i'm upgrading from a socket 478 pentium to socket 939 athlon 64, so i figured it'd be nice to upgrade the cooler too. definite temp drop, no joke, i'm very close to room temperate at times with this thing. current system temp is 82F(case only tells fahrenheit) and cpu temp is 87F/31C. highest i've ever seen it get is 41C after playing Brothers in Arms: Earned in Blood for about an hour nad a half. best part is it sucks the hot air right off the ram too, and shoots it all right out the back through my 120 case fan.