Well - $600 is enough to get some decent stuff if your only looking for CPU, MOBO, and RAM.
If SLI is the goal...then why not take the 750i FTW for $190http://www.newegg.com/Product/Produc...82E16813188026
A nice set of Ballistix for $75http://www.newegg.com/Product/Produc...82E16820148069
And then go for broke and grab a Q9450 for $360http://www.newegg.com/Product/Produc...82E16819115042
I mean - that's one way to do it....but there are literally hundreds of combos you could do. Maybe take a Q6700 and save $100 and then get the 780i.
The point is...what are you comfortable with? Is there a particular chipset that you've been happy with? Are you a fan of Asus, MSI, EVGA, etc.? Does your PSU support both 4-pin and 8-pin connectors? Are you limited by the size of your case?
A few more details about what your goals are might help. I mean - $600 is not chump-change and it would be awful to buy things that were meant for someone elses dream rig and not your own.