have the Seagate Barracuda V which is very quiet, and seems to perform well. Unfortunately I've yet to get other silent components like the PSU, so its efforts are mostly wasted on my setup, but I've seen the Seagate Barracuda IV in action on a PC that was completely silent.
I've Seagate Barracuda IV in my Pegasos. My PSU is not completely
silent but almost. Music for my ears when there is no noise at all
:-D