Anything made by SeaSonic (often re-badged by Corsair, Antec, etc).
I've had three SeaSonic PSUs now, and they are all quiet and reliable. You can sometimes grab youself a bargain too... my current PSU is
http://www.overclockers.co.uk/showproduct.php?prodid=CA-117-AN&tool=3
which I managed to buy brand new for £50 a year or so ago. The price has gone up ever since!
Ooh, I was looking at one of those this morning (the 80+ Gold?). Let me know what it's like when you get it. I'm undecided between a new one of those, or buying something used and doing a fanswap.
Have been told old TX were quiet, but new TX v.2 are not. Trust me on this I have 2; TX650 v2 and TX750 v2. Can hear them at system idle from 2.5 meters.Can't hear anything from my TX850 Corsair. I imagine it's the same with HX, AX etc.