Hi newcomer and welcome to the Tom's hardware forum.
1- What is your budget?
Mobo: Asus P6T Deluxe V2 or THIS
if the budget isn't important
GPU: GTX285 or better. Or 5850 or better
RAM: 6GB (3x2GB) CL7 or CL8
HDD: Spinpoint F3 1TB or SSD
PSU: 500W-600W if you only run a GPU, for SLI or X-Fire you need 700W