Not sure why so many are suggesting 750ti. It is a great card for a weaker power supply, but the op ha a 650 watt. Considering that, I think the gtx660 would be a better choice, and provide a more noticeable upgrade from the 650ti.
That said, considering the CPU and resolution, I am not sure an upgrade from the 650ti is really needed or worthwhile.
750Ti review is fresh on people's minds.
So it's the first thing they think of.