For bang-for-buck quietness:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835186033
These are what I use for my primary case fans.
Though a bit more costly, these are really good as well:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835214028
At full tilt they are slightly louder than the Arctic F12s, but I feel that they are more robust.
I have also had the privilege of using some of those Cougar Vortex fans. They performed really well, and they're about as quiet as the Enermax fans. On the downside, the PWM circuitry is bonkers; at 1000+ RPM, they make a noticeable whine. Buying only the 3-pin models aside, you can fix the problem with any hardware or software fan controller that will use voltage, instead of a PWM signal, to operate the fan speed. Just mentioning as an option, although your average buyer won't want to put up with the extra work.
EDIT: In case you were actually interested: http://www.newegg.com/Product/Product.aspx?Item=N82E16835553002