What budget GPU should i be getting ?

This is my current pc specs:

OS:Windows 7 64-bit

CPU:Intel Core i7-3770 @ 3.40GHz (8 CPUs)

RAM:16GB

GPU:Nvidia Geforce GTX 650 Ti.

My GPU is really holding me back from playing recently released games and i think its time for an upgrade. But problem is i dont have much money so im not sure which one i should be buying.