I built and tweaked this computer a few years ago to be powerful but inaudible over ambient noise. The CPU cooler is completely silent (passive), while the video card (Nvidia Geforce 9600 GT) settles down to inaudible right after startup. It was connected to an HDTV using a DVI->HDMI adapter (42" monitor!) and made for an awesome setup.
Intel Core 2 Quad Q6600 (quad-core processor) w/ Scythe heat-pipe passive cooler (Ninja Mini?), tweaked for heat reduction
4 GB performance RAM
Gigabyte GA-G33M-S2 motherboard
1 TB SATA hard drive
Nvidia Geforce 9600 GT graphics w/ 512 MB RAM
DVD burner and Blu-ray drives (includes PowerDVD 8 for Windows Blu-ray watching)
Glossy "piano black" finish Antec P150B Quiet PC Case with efficient power supply (See here
The box is currently a Windows XP and Kubuntu linux dual-boot. I can customize to some degree per request but don't have a license of Windows 7 for it.
My asking price is $500 but I'll entertain lower offers depending on how I feel about lugging it cross country come next week.
PS Thanks to spcr for the reviews i used to put it together in the first place!