All but the last of the cases profiled in this article will not work. They are designed for Atom-class processors. Far too small for proper cooling, and they come with miniature power supplies.
OP - you have a very specific need, as it turns out - few gaming systems will actually fit or function within a cabinet. If that's still your preference, I'd look at building a mini-ITX system.
You'd probably want to start with a motherboard like this:
http://www.newegg.com/Product/Produc...82E16813157238.
Then go for the 2500, not the 2500k processor, since you can't overclock:
http://www.newegg.com/Product/Produc...-073-_-Product. Don't worry, it's still wicked fast.
Then I'd probably just go straight for 8GB, because you only have two ram slots so you're limited as to upgrades:
http://www.newegg.com/Product/Produc...82E16820231417.
Then I'd probably pick up this Silverstone case:
http://www.newegg.com/Product/Produc...82E16811163171. It actually comes with a very good 450w 80 Plus Bronze PSU, so you'd be set with that. Hint: you can get free shipping at Amazon.
Then I'd pick up the Sapphire HD5850, which will fit in this system without a problem:
http://www.newegg.com/Product/Produc...apphire%205850
And you'll need a slim DVD burner, like this one:
http://www.newegg.com/Product/Produc...82E16827151221. Because it's designed for laptops, you also need this converter cable:
http://www.newegg.com/Product/Produ...2200374&cm_re=lp4_sata-_-12-200-374-_-Product
With that and the HD/SSD and cooler you've already picked, you're done. One sweet (and very small) gaming system. Comes to about $900 before tax.