tbh, atm, your most important component to buy will be the motherboard.
ensure it can take sli x 16 ... some only do it x8, then pop in a average ( ie cheap) dual core awesomeness e6600/e6700 would do for the moment, then plonk in the faster ( and cheaper ) cpu later
My system as it stands, is 1 year old, and consists of
1 x Intel core2duo E6600
1 x Asus pn5-e-sli Mobo
1 x Bfg nvidia 8800gts ( 640Mb)
4Gb of matched ram
Extreme Music XFI soundcard
random HD
and a slightly generic modular psu...
and the Asus mw226 22" widescreen monitor
I doubt mine would even cost £600 if it were to be built nowadays possibly £700 with the monitor...
All i need to do for my next upgrade, is either change out the cpu, or change out the gfx, but, atm, I dont think there will be a need within the next year...