depends on a lot of factors. a good GPU would be a 980Ti, however do you have a decent PSU/can you even afford it?
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As he said there is many factors involved in getting a graphics card.
If money is not an issue and you are wanting the best gaming PC possible- Titan X
If you want a more average gaming computer than runs everything you want- GTX 960
Or if you are not looking to game jut want a GPU that supports 1080p almost any graphics card will do
I recommend ASUS products, ASUS has always done me well. I use an ASUS R9 270x 4GB
Just figure out all the factors you want and do some research and then do some shoppping

Squidz wrote As he said there is many factors involved in getting a graphics card.
If money is not an issue and you are wanting the best gaming PC possible- Titan X
If you want a more average gaming computer than runs everything you want- GTX 960
Or if you are not looking to game jut want a GPU that supports 1080p almost any graphics card will do
I recommend ASUS products, ASUS has always done me well. I use an ASUS R9 270x 4GB
Just figure out all the factors you want and do some research and then do some shoppping

The 980Ti will perform about the same if not better than the Titan X for a fraction of the cost.

Just because it costs more doesn't mean it has better gaming potential.