I'm looking for an 80mm fan that produces < 21dB of noise. If it has a fan controller then I don't care what the max noise is, as long as it can go below 21 at minimum settings.
Noctua makes an 80mm fan. 17 dBa at full speed. If you use the included ULNA (Ultra Low Noise Adapter) the air flow is cut in half, but the noise is reduced to 7 dBa.
enermax makes a great 80mm quiet fan. check newegg. i believe it's like 18db or around there. i picked up 2 from the egg and they are perfect. one is my intake fan and other is on my cpu (amd 64 3000+) heatsink. very quiet and temps still low.