Well, me,I play games, but now that I've finished
Mass Effect 2
twice now( had to check out both endings) and
Bioshock 2
is not out just yet, so I build high level
AMD Dragon systems on paper. Whats a
Dragon system? pretty much every high end part AMD has. as in:

ASUS R.O.G. Crosshair III Formula ATX AM3 790FX/SB750 2XPCI-E16 3XPCI-E 1XPCI CrossFireX Motherboard
Processor

AMD Phenom II X4 965 Black Edition Quad Core Processor AM3 3.4GHZ 8MB Cache 125W 45NM
Video Card

XFX Radeon HD 5870 850MHZ 1GB GDDR5 4.8GHZ 2XDVI HDMI Display Port DIRECTX11 PCI-E Video Card
OR

XFX Radeon HD 5970 725MHZ 2GB 4GHZ GDRR5 2XDVI Display Port PCI-E Video Card
ether one will be just fine. but the 5970 is a duel core card. but its also a big card at 13.5" long, so you may need a bigger case.
Memory
2X
Corsair XMS3 Dominator GT CMG4GX3M2B1600C7 4GB DDR3 2X2GB DDR3-1600 CL 7-7-7-20 AMD Bemp Memory Kits
Ultra-high performance 4GB DOMINATOR GT kit for AMD Phenom IIDDR3 processors and platforms. 1600MHz, 7-7-7-20, 1.65V with AMD Black Edition Memory Profile (BEMP Support). Includes Corsair Airflow Fan.
Dominator kit also supports AMD's Black Edition Memory Profiles (B.E.M.P), which allows for the aggressive latency settings to be automatically configured in Windows using the AMD OverDrive™ software utility
Case

Coolermaster CM 690 II Advanced ATX Mid Tower Case Black 4-5.25 6-3.5 INT bays
CPU Cooler

Corsair Cooling Hydro Series H50 High Performance CPU Cooler System LGA775 LGA1366 LGA1156 AM2 AM3
This unit will give you room for the memory coolers(fan) and give you more room to play with over clocking your rig
Power supply

Corsair TX850W 850W CMPSU-850TX 12V 70A 24PIN ATX Active PFC 140M Fan Power Supply
Optical

LG CH10LS20 Bluray Reader & DVD Writer Combo Drive 10X BD-ROM 16X DVD-RW Lightscribe
OS Hard Drive

Intel Gen 2 X25-M 80GB 34NM Postville 2.5IN SSD SATA Solid State Disk
Game and App Hard Drive
2 X 
Western Digital Velociraptor 300GB SATA 10000RPM 16MB Cache 3.5IN Hard Drives
in a RAID 0 will give as much performance as a spining disk can and more size at 600GB
Operating System

Microsoft Windows 7 Professional Edition 64BIT DVD OEM
Case mod / Temp Display

NZXT Sentry LX High Performance Aluminum Fan Controller Black W/ LCD Dual 5.25IN
Just to watch the temps inside, and if you want, run up to 5 fans. plus the handy clock helps for when your in game, and wanna look at the time
Keyboard

Steelseries Merc Stealth Illuminated Gaming Keyboard W/ Dedicated Gaming Terrain
Mouse

Steelseries Ikari Laser Professional Gaming Mouse
Mouse Pad

Steelseries Qck Cloth Mouse Pad 11.2X12.6IN
Headset

Steelseries 5H V2 Headset HI-FI Headphones 16-28000HZ 40OHM
Think i like Steel Series? oh ya
Webcam

Microsoft Lifecam Cinema 720P 16:9 HD Webcam Retail Box Auto Focus Noise Cancelling Microphone.
And Monitor(s)
3X
HP Compaq LA1905WG 19IN Widescreen LCD Monitor 1440X900 1000:1 5ms VGA DVI-D HDCP DisplayPort
Why 3? the system you just looked at has
Eyefinity. so you can span your desktop to all 3 or play games on all 3. why these 3? well, so they match for one. and the other thing is these monitors are the cheepest monitor with built in Display Port yet. and i dont have room for huge monitors. to get the eyefinity working, you need 1 displayport monitor and 2 of any other port the card has on it. 2 x DVI-D, 1 x HDMI, or a $99 active display port adaptor will be required to adaptor the display port to any thing else.
so just around $3600 you can have a smoking fast gaming rig, that also looks good