^Not a great build. You've got an H67 chipset and a CPU that can't be overclocked, despite having a great GPU. While overclocking may not be desired by the OP, the H67's features are also useless. Considering that P67 boards aren't much more expensive (dual PCIe 2.0 8x/8x ones start at $150), and the "K" version is only $19 more, there is no reason not to spend the little extra for the option. Besides, overclocking the Sandy Bridge CPUs is so easy, you should always at least consider having the option. You may not want to overclock now, but it's a good option to have when you want to tinker a little.
Also, having 8 GB in a gaming build isn't necessary. Not only that, but those are slower sticks. If I was getting a 2x4 GB kit, I'd get this
Patriot 2x4 GB 1600 mhz CL 9 for $80 with promo code. Or one of G.Skill's Ripjaws or Ripjaws X sets at $100.
The change from ATI to nVidia is based entirely on the budget for the GPU. The switch from AMD to Intel is due to the budget and the fact that the new Sandy Bridge CPUs offer amazing performance.
As for having the extra cash, I'd use what's needed on the i5-2500K and P67 board I mentioned. The LGA1155 boards are coming out slowly. MSI's already got several available on Newegg. If I had to buy a LGA1155 board now, I'd pick the $180 one.
The card I'd choose to fill out the build is the HD 6950 2 GB as well. You can flash the BIOS and make it an HD 6970.
So here's the full build (most links are above):
CPU: i5-2500K
Mobo: ASRock P67 Extreme4
RAM:
Patriot 2x4 GB 1600 mhz CL 9. I know I said 8 GB isn't necessary, but it fits in the budget and there isn't anywhere else to spend that extra $40...
GPU: HD 6950 2 GB (the MSI one wasupmike linked to)
HDD: Samsung Spinpoint F3 1 TB
Optical: Cheapest SATA DVD burner you can find
That total is $789 after rebate.
I included a Crossfire enabled board, but the 600W Thermaltake (which isn't good quality) won't be able to handle that. You should consider upgrading that sometime. I'd suggest either
Corsair's 750W (non-modular, $80 after rebate) or
XFX's 750W (modular, higher efficiency, $106 after rebate and shipping).