My Antec EarthWatts 500W is pretty quiet. Mine is the old model (EA-500) which was made by Seasonic. Anyway, I had the oportunity to test a month ago the new EarthWatts 500W (EA-500D) which is made by Delta Electronics, and it's very quiet too. My overall impresion was that the new Delta model performs even better than the old one. Anyway, the final level of noise depends on the load of the system.
The Earthwatts 650W (EA-650) is a very good PSU with an incredible price/performance ratio (85$ newegg). It presents a really quiet 120mm fan. It's an ADDA AD1212HB-A71GL which is rated at 0.37A at 12v and is capable of moving 85.2 cfm generating up to 39 dBA at its maximun speed (2200RPM). It's the same quality fan that comes with the Corsair HX series (520, 620 and 650) and the TX650 PSUs (all of them are made by Seasonic).
It has a good efficiency (80 Plus certification), very good voltage stability (voltages very close to their nominal values) and good ripple and noise supression on its outputs.
Unfortunately, it's not a modular unit, but if you take in mind the price...
In summary, it's a quality PSU which performs quiet, although is not the quietest PSU in the market (the Antec Signature is one of the very best PSU you can buy if you want silence).
On the other hand, as I wrote in the last post, you CAN'T run a fanless PSU in a fanless case. That is not possible. You need a decent airflow inside the case to remove the hot air from inside the case. There are some internal components in a computer (cpu, mobo, HDs,...) generating heat and you must to take it out from the case. If not, the heat builds up inside the case increasing the temperature. Take in mind that the SILVERSTONE nitjar requires an internal case air temperature of 25°C (or less)...If you live in Alaska or Russia, go ahead, but if it's not your case, install, at less, one exhaust fan in your case (an intake fan would be recommended, but it's not necessary).
Anyway, this is just my opinion.