I am a firm believer in Bang For My Buck, so while my gaming rig is not as beastly as some listed, it Gets The Job Done. I can run all my games at highest settings for a 1920x1080 monitor, including Metro: Last Light and Tomb Raider. Pretty much all of it bought from Newegg, most of it at different times as a rolling upgrade.
ASUS M4A78T-E mainboard
AMD Phenom II X4 965 Black 3.4Ghz
Cooler Master Hyper 212 EVO CPU cooler
16 Gb G.Skill Sniper DDR3 RAM
WD Velociraptor 600 Gb boot drive
WD Caviar Black 750 Gb storage drive
ASUS Geforce GTX 660 Ti 2Gb video (my latest upgrade)
Antec Earthwatts EA750 PS in a venerable Antec SLK3700-BQE case