Nexus has announced its 140 mm Real Silent case fan.
The fan features a maximum rotational speed of just 1,000 RPM. At this speed, it makes 19 dBA of noise and pushes through 46.87 CFM in a non-restrictive environment. Sadly, the fan is not PWM controllable, and the starting voltage is 8 Volts. Therefore, it is unlikely to work on a 5 Volt line either for an even lower rotational speed.
The unit will hit the market any time now, packing a 3 year warranty, for an unknown price.