CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor ($189.99 @ Microcenter)
CPU Cooler: Corsair H80i 77.0 CFM Liquid CPU Cooler ($73.99 @ Amazon)
Motherboard: ASRock Z77 Extreme4 ATX LGA1155 Motherboard ($134.98 @ Amazon)
Memory: Corsair Dominator GT 8GB (2 x 4GB) DDR3-1866 Memory ($86.67 @ Amazon)
Storage: Sandisk Ultra Plus 256GB 2.5" Solid State Disk ($169.99 @ Amazon)
Video Card: Asus GeForce GTX 770 2GB Video Card ($399.99 @ NCIX US)
Power Supply: SeaSonic 650W 80 PLUS Gold Certified ATX12V / EPS12V Power Supply ($127.98 @ Newegg)
Total: $1183.59
You didn't mention a budget, and this doesn't include a storage drive, case, keyboard, mouse, OS, or monitor, but this setup will serve your gaming needs for a long while