my main machine, hooked up to my TV across the room via HDMI and into my stereo system (my 'main' monitor and kb are across the room with 35ft cables):
Asus K8n-dl motherboard
2x Opteron 290s (2.8GHz Dual Core software downclocked to 1GHz, set to ramp up when it hits 80%+ CPU in small increments until it's no longer at 80%, cut CPU temperature by 20*C)
9GB PC3200R ECC Ram (4x2GB, 2x512MB, 5GB on CPU0 and 4 on CPU1, am pondering changing it to 8/1)
Radeon HD 4650 (40$ budget card, wanted just anything quieter and cooler than my x1900 AIW whose video stuff isn't supported under XPSP3/Vista/7)
22in shitty widescreen LCD @1680x1050 over VGA as my main monitor (it was a gift, and haven't wanted to upgrade yet)
47in LG LCDTV 1080p via HDMI for videoMixVibes USB U-Rip22
(I was sent this for review and gave them a 2 page list of bugs with the software, they said thanks, please don't put out a review, and that they'd work on it. That was 18 months ago and the software was discontinued =P hardware works fine)
Main HDD: 4x 72GB 15K SAS drives in Raid 5 on a Promise FTTX4650
Old Main drive: 150GB SATA WD Raptor 10K
Storage: 750GB WD Green SATA
XBOX HD-DVD drive for playing, and Samsung Slimlime DVD burner for burning.
The case is custom built and unfinished. It's the reason for all the usb stuff (sound, and optical) as I intend to have the case be sealed/soundproof.
Additionally I have a box running FreeNAS with 2x 1.5TB, a 750GB, and a 500GB SATA drives and 2x300GB IDE drives for a total of about 3.8TB of space. I built this box to: 1) be able to turn off my main machine without losing access to everything on it, 2) have less hardware to worry about in my main machine/ less heat/less noise, 3) I was able to stuff it in a closet to not have any impact noise-wise.