"But you're gonna find it hard to get a hard drive that's ultra-quiet, and even harder to get a silent PSU"
I 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.
