If you really want to OC, then you will need to get the Intel i5-2500K which will be $30 more. Also, you will need another CPU cooler, probably running an addition $30-$50. And if you OC, you might also want a more powerful PSU.
SLI (for NVIDIA) and Crossfire (for AMD) is where you can have two of the same GPUs working together for increased performance.
If you are able to bump up your budget, you could get a more powerful GPU that will run games better.
This was just a quick build and some people may be able to offer some more advice and help you save a little more money.
EDIT: Just swapped out the mobo for a different one to allow for a more powerful GPU.
Total comes out $757, pretty sure this time around
And after mail in rebates, that should bring it down to $732.
Again, I apologize. I messed up on adding things up, totally my fault.
This build should do well in gaming. Although the budget does not allow for a quad core, games do not really take advantage of multiple cores. The i3 has the same clock speed as the i5 I mentioned before. Also, this GPU will still handle games really well. Let me know if you have any other questions.