Building Quieter Computers

So, as I suspect many of you have, I've got a home office that I probably work from for 2/3s of my working time, as I'm often working in the non-trad. office hours as well. It's nice having this space in my home, but the fans from the desktops are so loud, I feel as if I'm standing in the middle of O'Hare's runways. Anyone out there know of power supplies with quiet fans? CPU fans that are extra smooth?