Building a Mid-Level Gaming Computer

Hello, I am trying to build a new pc for the upcoming Diablo 3 and to play Mass Effect 3. I do not care to play everything in its highest settings because I know I can't afford it. I am a casual gamer looking for a mid-level rig at said price level, if you can get it cheaper then that's better. If something is a little more I wouldn't mind hitting $650ish to get something that makes a big difference. All in all, I want as much performance I can get out of the $600. Thanks for the help! Let me know about your ideas  

I have: Keyboard, Mouse, OS, Monitor, and an M-Audio Speaker system, so don't those.

EDIT: I apologize, I was excited reading what the users on this forum had to say and their knowledge in the subject I posted without looking at the rules.


Approximate Purchase Date: (e.g.: this week (the closer the better))

Budget Range: 600-700

System Usage from Most to Least Important: Gaming, Movies, Photoshop, Internet

Parts Not Required: (e.g.: keyboard, mouse, monitor, speakers, OS) **Include Power Supply Make & Model If Re-using**

Preferred Website(s) for Parts: Newegg.com, tigerdirect.com, microcenter.com Anywhere with good deals  

Country: U.S

Parts Preferences: No Preference, maybe if we could get in an i5 processor? But that would probably take me out of budget, let me know!  
Overclocking: Maybe

SLI or Crossfire: Maybe

Monitor Resolution: 1680x1050