OK, so my rig is a 'bit' dated (by a couple of generations of hardware now), but I can still play FEAR, BF2142, Prey, and HL2 at 1280 x 1024, with most of the cool lighting effects, averaging around 40fps.
Athlon XP 3200+ 2.2GHz (overclocked @ 2.4 GHz)
DFI LANPARTY NFII Ultra B nForce2
2GB Corsair TWINX3200C2PT 400MHz DDR
EVGA GeForce 7800GS KO ACS3 256MB GDDR3, yep thats AGP!
(2) Western Digital WD1600JD 160GB SATA in RAID 0
(2) Sony DRU800A 16x DVD Burner
Thermaltake Armor VA8000SWA Silver Full Tower Case
AeroCool GateWatch-SV Silver LCD display
Viewsonic VX924 19in LCD Monitor
Microsoft Natural Ergonomic Keyboard 4000
Razer Diamondback Chameleon Precision Gaming Mouse
XP Pro SP2 - stripped down to the eseentials
And the real reason I haven't upgraded, is the water cooling setup on it. I think I spent more on the water cooling than I did on the CPU, Mobo, & RAM combined!
DangerDen Copper TDX AMD CPU Block
DangerDen Maze4 Chipset Block
DangerDen Koosah GPU Block
Black Ice XtremeII radiator
4x 120Mmm Sunon Fans in Push-Pull
Eheim 1260 600GPH pump
DangerDen Fillport Reservoir with 2 Delrin fillports for fill and bleeding
Tygon 3603 1/2" OD Tubing
DangerDen MCT40 Non-Conductive Cooling Solution
System runs at a stable and cool 30C-33C under load