usually, for rendering stills and animations, by far the most important thing is the processor.
the video card plays no part in the actual rendering BUT it will help you a lot WHILE modeling, because manipulating and viewing your scene inside your modeling software is done mostly with the graphics card.
I would suggest you get a top tier processor, maybe a 3770K and a water cooler, a nice Corsair H100, and read a bit about overclocking and you might get anywhere from 30 to 40% improvement over the basic processor.
also depending on what you are doing, ram can be important, I have 16Gb and they fill up fast smoothing my models in Mudbox.
this is only the basics, if you want some more help you should always give an proximate budget for your PC, tell us more or less when you plan on buying, programs you will use and other uses for that PC.