I would choose between these the two for a quiet unit:
NZXT Hale90 750W 80Plus Gold Modular $140http://www.amazon.com/HALE90-Power-Supply-Modular-HALE90-750-M/dp/B003YFIUEG
The fan speed on maximum load has been measured at 890RPM.
Corsair HX750W 80Plus Silver/Gold Modular $135http://www.amazon.com/Corsair-Professional-750-Watt-Certified-Compatible/dp/B0029F21LK/ref=sr_1_1?s=electronics&ie=UTF8&qid=1337937011&sr=1-1
The fan speed of the 850W version on maximum load has been measured at 1376RPM.
The fan speed of the TX650M on maximum load has been measured at 1535RPM.
Seeing as the 750W version has a higher noise rating I would expect the maximum fan speed to be higher.
However the TX650M's fan was very slow spinning (~800RPM) until a 60% load and only started to accelerate after that.