$600 and future proof, eh. Well, hm. This is what I came up with.
Case - NZXT Source 210 $39.99
*CPU - AMD FX-6350 Vishera 3.9GHz Six-Core Processor $139.99 OR AMD FX-4350 Vishera 4.2GHz Quad-Core Desktop Processor $129.99
RAM - G.SKILL Ripjaws X Series 8GB DDR3-1333 CL7 $64.99
Video Card - PNY GeForce GTX 660 2GB 192-bit GDDR5 $179.99
*HDD - Western Digital Caviar Blue 1TB 7200RPM $69.99 OR Get the 500GB drive to save $10 (There's a drop down box to select that)
Motherboard - MSI 970A-G43 AM3+ $69.99 + $4.99 Shipping
Powersupply - CORSAIR CX430M 430W 80 Plus Bronze $49.99
* Indicates where you can choose a different item to save money
Total - $619.92 (6350, 1TB HDD) (You can save $20 by getting the 4350 and the 500GB HDD)
Please don't stone me for breaking the budget!
Don't know how "future proof" that will be, but for $600 it seems pretty good to me.