Motherboard Asus P8Z68-V PRO/GEN3
Good board,got one myself.
Processor Intel i3-2120
Not quite up to the job ,benchmark click here i5 2500k recommended.
RAM Komputerbay 8GB
Not heard of this brand, suggest you go with Crucial , Corsair or similar.
GPU Sapphire HD 6870
HDD WD Caviar Blue WD3200AAKS
1 TB HDD is standard nowaday.
Optical Drive Samsung 16X DVD-ROM
Get a DVD-rw instead for roughly the same money.
Case Zalman Z9-U3
Ok-ish budget case, make sure there is room for the Sapphire HD 6870 which is over 9" long, you might struggle to put the 2 x 6pin power cables in if the power connectors are at the back of the card.
PSU Corsair CMPSU-500CXV2UK 500W
650W PSU is recommended.