What brands do you have access to?
Ideally what you are looking for is 6gb or 3x2gb of ddr3 1600 ram.
psu from a good brand be it corsair or pc power and cooling in the 650 to 750watt range.
gpu gtx280, gtx285, ati 4890 or you could save cash going with gtx260 or ati 4870. (evga or xfx)
i7 920
1336 x58 motherboard from asus, biostar or evga.