It basically comes down to personal preference and how much your budget is.
If Nvidia
Get a GTX 760 if you want to upgrade when their next set of cards come out
Get a GTX 770 or 780 if you don't want to upgrade come the refresh
For AMD,
One of the new R9 or R7 cards should be fine. Compare the models for what you want.
However, you can just survive on the Intel HD graphics for the time being if you want to save money and wait for the next refresh cycle for AMD/Nvida. It should be enough for around 2x IR in most games
If Nvidia
Get a GTX 760 if you want to upgrade when their next set of cards come out
Get a GTX 770 or 780 if you don't want to upgrade come the refresh
For AMD,
One of the new R9 or R7 cards should be fine. Compare the models for what you want.
However, you can just survive on the Intel HD graphics for the time being if you want to save money and wait for the next refresh cycle for AMD/Nvida. It should be enough for around 2x IR in most games