Installed a Zalman 460W PSU in a customers PC a few days ago, and he's very happy. Its a little low on its 12V rails (Typical from zalman supplies). The voltages are strong, but its only got two 12v rails one rated at 16Amp, and the second at 18Amp. Still I guess that is 408watt's combined power 12V, from a 460W total isnt too bad. Afterall you still have the 3.3V for the memory, and 5V is still used for hard drives/optical drives, so although 12V is the most important, its not unreasonable to have some power left over for the smaller power rails.
Anyway more than enough to power a single 8800GTX type graphics card, and quadcore cpu system.
Quiet.. hell yes. When its cool it actually turns its fan off completely, and when the system is lightly loaded the fan is running so slowely its inaudible. As the internal temperatures rise it adjusts it's cooling, but at no time could I hear its fan above the CPU fan anyway. Good heavy PSU, seems well constructed. Peaking through the grill on the back, the silkscreening on the main circuit board indicated that its designed to be used in PSU's rated from 350W to 550W, obviously different componants installed to give higher power ratings.
I've owned Zalman PSU's in the past, and I would give it 9/10.
As already said Corsair and Seasonic are both excellent, but the Corsair 420 was out of stock at OcUK, and they dont stock a lower powered Seasonic. So I thought I would give the Zalman a go, and it looks like another solid product from Zalman.
My current system uses a Seasonic S12 500W PSU, and its very quiet, but the Zalman's quieter.