I'm not going to add any specific recommendations, I'd need to know your budget and whether you decide to upgrade CPU/MB also. However, I will add this and I recommend very strongly you follow my advice:
Do NOT buy a cheap graphics card ONLY because your current CPU and MB are going to bottleneck it. If you can afford a 770 superclocked or a 280x then you should get the best GPU for the money you can find. Then save up some money and get a new CPU/MB and RAM a little down the road. If you buy now based on your current system and get a card that is already somewhat outdated, when you decide to upgrade the rest of your system you'll just end up replacing the new graphics card again and wasting money.
Whenever I buy a GPU and NOT a whole machine, I always get one good enough that I'll use it in my next build without upgrading. Then, depending on how good or bad the system performance is I can always upgrade the video card midway between full builds or hold off. That way you're getting the most use out of a single graphics card and not wasting money on stop-gap upgrades.