Here's a list of parts for a pretty good build as of now;
CPU
AMD Phenom II x6 (~$200) or Intel i7 4770k ($339)
GPU
AMD Radeon 7970 ($300) or NVIDIA GTX 770 ($400)
RAM
Up to you really, but I wouldn't get less than 8GB. 8GB ($80) 16GB ($160) 32GB ($400)
HDD
Up to you, I have a 2TB. ($120)
SSD
Optional, can increase performance in high-end games.
Board
If you get the Intel CPU, this one will work.
GIGABYTE Z87X-UD4H ($190)
If you get the AMD CPU, this one will work.
Gigabyte 990FXA-UD3 ($140)
Prices are from Newegg.com