well it all depends on your budget, if you have no problem with budget then go with i5 2500K a Z77 chipset motherboard (either AsRock for the cheapest decent one, then Gigabyte, Asus, or MSI are the bigger brand out there)... then go all out with the GPU (like HD 7870, HD 7950, GTX 760, or GTX 770). Although that will be about $800~$1000...
or maybe you can go with i3 3240 + h77 chipset mobo + GTX 650Ti Boost (around $350~400 ish) ???