Nexus specs look good, but from what I could find out the high speed range coupled with the stiff clear plastic frame doesn't make for a quiet fan.
I've seen the Arctic Cooling fans but I've got no personal experience with them. (not enough posts to add a link)
There does seem to be a lack of choice with PWM fans, my plan was not only to put one on my Scythe infinity but to also use one as a rear case fan.