I've usually had Nvidia cards myself, not because I had anything against Radeon, just more familiarity with their product line. From what I've heard Radeon is sometimes slow on putting out drivers updates, but I don't know if that really has any serious implication on performance or not. I tend to doubt it does.
Well, as far as being back in the loop for computers, right now the absolute best gaming CPUs on the market are Intels. Specifically the I5-2500k, if you could find a way to get one of those in your budget, that would be your best bet, but with 800 dollars to fit, the only way I could see you pulling it off is to go cheaper on the video card, and for a gaming system, that isn't a hot idea, since just about any CPU is going to handle games.
Intel has a pretty big price gap between their dual cores and their quads unfortunately.
Their dual core i3s work pretty good and cost about the same price as the Phenom II I recommended, but its limitations are the 2 less cores. This may or may not be a problem playing online multilayer games (since Online play is more CPU intensive than Single Player, or as new games come out (Since right now I think BF3 is one of the only game that can use more than 2 cores).
I think I'd lean more toward more cores at this point. My gaming is trending more toward single player (RPG's like Skyrim, Deux Ex, etc) than MMO's and online play.
If I have money to spare, I'd prefer to put that extra money in the GPU if it's doable so I'm perfectly fine with the Phenom. Although seeing how it's not a huge gap between the 6870 and the 560's, there really isn't a whole lot of room there unless I want to bump up the budget to 850, then perhaps some other cards may come into play?
That case is perfect also, I've always done flashy cases in the past but I'm getting older, the case should reflect a more rugged, dare I say more mature, aesthetic.