Graphics Card - Pick your GPUs! Some graphics cards cost a fortune but don't hash much whilst some are more reasonable but use more power. Ultimately its a balance between how powerful you want your rig to be and how much you want to spend - but a word to the wise - make sure you pick an efficient GPU. You can buy second hand GPU's from reputable providers such as GPU Shack - be careful though when you buy them off a street corner as often they have problems that you won't see until you get the card home and plugged in.
We have a list of GPU's here that you can sort through and work out what fits your budget.
RE: For those thinking of getting into Ether mining read this