I built mine a year and a half ago for just under 1k. Stuff I re-used: monitor, keyboard and mouse.
I didn't go hog wild:
1 x COOLER MASTER HAF 922 RC-922M-KKN3-GP Black Steel + Plastic and Mesh Bezel ATX Mid Tower Computer Case with USB ..
1 x ASUS P8P67 PRO (REV 3.1) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 ATX Intel Motherboard
1 x EVGA 01G-P3-1561-AR GeForce GTX 560 Ti FPB (Fermi) 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support ...
1 x CORSAIR TX Series CMPSU-750TX 750W ATX12V v2.3 SLI Ready CrossFire Ready 80 PLUS BRONZE Certified Active PFC Compatible ...
1 x Intel Core i5-2500K Sandy Bridge 3.3GHz (3.7GHz Turbo Boost) LGA 1155 95W Quad-Core Desktop Processor Intel HD Graphics ...
1 x G.SKILL Ripjaws Series 16GB (4 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9Q-16GBRL
2 x COOLER MASTER Megaflow 200 R4-LUS-07AR-GP 200mm Red LED Case cooler
At the time it was $993 not counting tax and shipping. I have had stable, fast gaming out of it ever since.