Mine is just an upgraded Dell Optiplex 745, the CPU, mobo and cooling are all stock. It manages to play everything I throw at it.
CPU: Core2Duo E4300 1.8ghz
RAM: 4gb PNY in dual channel
HD: Seagate 750gb, Seagate 2TB
PSU: Thermaltake 600 watt
GPU: Gigabyte GTX 550 Ti 1gb
OS: Win 7 64-bit
Audio: Video card via HDMI into my TV then out to my soundbar via toslink.
It's not super amazing but it still blows my PS3 and 360 away.
Toshiba 50" LEDTV (ISF-certified calibration) | Sony 24" LED 3DTV | Monster HDP1800 Power Conditioner | Harman Kardon AVR1700 | Polk Audio F, C, R & SUB | Audio Technica LP60 Turntable | PS3 (1.5TB) | Modified Dell Gaming PC