CPU: Intel Core i7 870 (45nm, Soket 1156, 2.93GHz)
motheboard: Intel DH55HC (intel H55)
RAM: EK Memory DDR3 10600 2GBx2EA
vid card: GIGABYTE GeForce GTX 460 1GB WindForce or ZOTAC GeForce GTX 460 1GB
hard disk:Seagate Momentus XT 500GB
power supply:Acbel iPower 500
case:Bestech Guardian
monitor:Orion TopSync 24
This is by no means an official specs listing for the FINAL version of DIablo 3, but it does give you an idea of what you can look for if you are shopping now.
IMO the GeForce 460 GTX will be the "sweet spot" video card for D3, so far as max performance for best value is concerned.
And any current or previous gen Dual or Quad-Core CPU running at least 2.8ghz will suffice.