Hello. What is your budget? Also, what power supply are you using? What case? Here are a few awesome options, I would buy if I was in your shoes.
Nvidia Evga gtx750:http://www.amazon.com/EVGA-GeForce-Dual-Link-Graphics-01G-P4-2751-KR/dp/B00IDG3NDY/ref=sr_1_1?ie=UTF8&qid=1403460783&sr=8-1&keywords=gtx750
Nvidia Evga gtx 750ti:http://www.amazon.com/EVGA-Superclock-Dual-Link-Graphics-02G-P4-3753-KR/dp/B00IDG3IDO/ref=sr_1_1?ie=UTF8&qid=1403460825&sr=8-1&keywords=gtx750ti
The gtx750ti is faster, but more expensive. If these are too expensive, look at this. It is not as good as either, but still ok.
Nvidia gt640:http://www.amazon.com/EVGA-GeForce-2048MB-Graphics-02G-P4-2643-KR/dp/B0086UXQES/ref=sr_1_1?ie=UTF8&qid=1403460900&sr=8-1&keywords=gt640