DeltaAFB1212SHE-PWM 120mm x 38mm 4pin PWM+Tac Sensor, Extreme Hi-speed 3700 RPM, 151 CFM Case Fan

I love this fan. It is not noted in the listing, but the specs for this fan is rated at over 14 mmH2O of pressure... that is extremely high for a case fan, meaning it works well in constricted airflow environments. It runs as low as 20% on 4-pin PWM control which give you about 500 RPM, and is near dead silent at that speed. Sure it's loud at full speed, but you get a TON of air, and you can always slow it down if you want lower noise. Other "low noise" fans are just slow, and with this one, you at least have the option of delivering massive air when needed. You can't do that with the others.