For $300 you can get a 7950 or a 660ti.
Unfortunately your power supply won't work for either, and the cpu would probably bottleneck both. I recommend either the 650ti or the 7770 for you.
Thanks for the reply,
I have a couple questions. I have been looking at the 660ti. What power supply would I need to run that? And If I got the 660ti would it work well until I get the money to upgrade my CPU? Because I plan on upgrading everything and make it a high end machine, just starting with my graphics and power supply.