Z77 ATX Motherboard of medium tier e.g ASUS P8Z77-V or equivalent from other brand.
Corsair Dominator or Vengeance 2X4GB DDR3 RAM
128gb SSD OS, 1TB HDD games
650W PSU Corsair HX or TX
Fractal ARC define Midi R2 Case
LG IPS 23" monitor (Tend to be cheap over here).
Window 7 Home Premium
Leave the left over to DVI or HDMI cable, extra case fans, thermal paste, mouse and keyboard.
The HIS HD7870 should be fine.
A member here is getting some high temperatures in dual card config though.
My HD7870 gets up to 80degC max in stress tests and 65-75degC in games.