Antec 900 case
Intel i7 930 @ 3.9ghz (waiting on a 970 to come in atm)
ASUS P6T (X58) running a custom BIOS
Measly 12GB DDR3 @ 8-8-8-20 clocks (Just ordered 24GB of slightly faster RAM a week ago, waiting for it still) - I never bother OC'ing RAM. It's boring, and hardly gives a useful benefit for the lifetime cut it takes.
Currently using 2 craptastic gfx cards - GTX 460 and GTX 260. Mainly just so I can run my 3 displays (5 again soon) - These are being upgraded to GTX 480s in Tri-SLI sometime this week/next week. (Found some EVGA's for $250 a piece, couldn't pass it up)
Also have a SoundBlaster X-Fi Platinum sound card that rarely gets much actual use. (I'm not a big 'sound' guy. So long as it's clear, it's good enough for me) - The card is PCI if that tells you how old it is. (Yes, it's the one with the front-mounted MIDI/Optical/S-Video ports, and a remote control)
Also running 4x HDDs of varying sizes. No RAID configuration. (2 of the HDDs run other OS's, the other 2 are Windows, with multiple VMs)
Most I've tried running on this current rig, was 40 WoW's when I got into a process-creation loop by accident. It handled it fine. Can't say how well it performs with all of them in game though.
This rig is a dev rig, so I'm not shooting for top-notch gaming performance. What I get is more than I need in most cases.
Protip: when actually gaming, the GTX260 card serves as a dedicated PhysX processor.