Might want to follow the guidelines in the link in my signature. We need a budget to do any real good.
For a GPU, I would recommend either the HD 5770 ($160) or the HD 5850 ($300), depending on what you want to spend. The 5770 is good for gaming now, but might be a little underpowered later on. The 5850 will be good for a while.
If this is only a gaming computer, you might want to consider using the i5-750. The cheaper price on the CPU, mobo, and RAM will allow a more expensive GPU, which is more important for gaming.
You'll also want to drop the CM Scout, 10.5" max gpu cards. If you ever do decide to upgrade to a 5870 (or Fermi, or any large card) you're either going to have to dremel out the hdd cage or buy a new case.
Check out CM 690II, Lancool K-62, Antec 902 for cases that have all the features of the Scout, the same price range, and support larger cards.
If you're super ambitious and want a monster like a 5970, Antec 1200 or CM HAF 932 come to mind.
Or you could just buy a behemoth of a case like Corsair 800D or Silverstone TJ07.