I would disagree with stoney about the ram
i frequently use as much as 5.5GB of ram and 1600MHz is noticably faster than 1333MHz
it is also only $40 more which is not a whole lot in the computing world
The issue I disagree on is the CPU, the OP stated he had no intention of overclocking and even if he wanted to leave that option open for the future, the i5-2500k is a better choice.
The i7 is faster, but there is no real noticable difference in games. It really only excels at heavily threaded programs....which SC2 is not. The $100 dollars price difference is better used toward things like a copy of Windows. I didn't see anywhere that the OP stated he had a copy of Windows or planned on using Linux, so i have to assume he needs it.
Read the $200 and up page of the link above, anything over the i5-2500k is overkill / bragging for gaming as there is no real performance gain.
As to the video card Stoney recommended, I'm playing SC2 on Extreme with a Radeon 6870, so a 6950, which is a good amount more powerful, is a bit overkill at this time, why pay $200 dollars more for performance you likely wont notice unless the system requirements go way up. The money could be used to get other parts of higher quality or speed.
For me its not about getting the latest and greatest on a few parts, its about getting a powerful, balanced (price/performance) machine that will do everything I need and want...and then some.
@Stoney - You do realize that you recommended a nVidia video card and a Mobo that only supports Crossfire. If the OP decided to used 2 or more cards later on, he'd have to replace the video card instead of just adding one? Thats another perk the Z68 playform has that the older X58 had, support for SLI and Crossfire.