Welcome to the forums.
Currently the top of the tree for pertofrmance PC's are Intel, so bearing that in mind and not going bananas with your budget
Asus P6T SE
Intel i7 920
Fenrir Titan HSF
Samsung Sping Point F3 1TB x 2
3 x 2 gb DDR3 triple channel memory kit
Corsair or OCZ PSU
Nvidia 285GTX or ATI 5770 video card
just leaves you choice of CD drive and operating system.