I would recommend getting a larger case, it may seem large, but the length isn't so great, so if you want a bigger gfx card it is going to be a tough fit, as it looks like you get maybe an inch or so past the mobo to the hard drive cage, so go something like this one: Newegg.ca - RAIDMAX SMILODON Extreme Black ATX-612WEB 1.0mm SECC Steel ATX Mid Tower Foldout MB Computer Case
It has large length so you can have good space between your mobo and hdd cages, and if you get longer ones you could mod it so you push your hdd's more into the cage, or if you are daring you can easily remove it as it is removable and just have pure gfx card room, then you can get any gfx card known to man, and also for hdd i would go with a western digital caviar black since your board has sata 6gb/sec:Newegg.ca - Western Digital Caviar Black WD1002FAEX 1TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive
this hdd supports it,
For a gfx card go something sapphire, or HIS each is very well renowned and they both only go for ATI cards and are great aftermarket card makers, such as HIS' Ice Q design and Sapphires Vapor-X technology, personally I have a 5850 Vapor-X and it runs coooool, and so you could go get a 5770 for around $150-200 (rounding up) or you could go to 5850 (approx. $300) skip the 5830 (250-310) bad things about 5830's they pretty much 5850 and 5870 with more processing units turned off 1120 vs 1440 vs 1600, the 5850 performs a lot better, and you can get a better card for 50 to almost the same price as the worse performer, and also the stock 5830 is longer than the stock 5850, is slower, and takes up more power, but the choice is yours.
Have fun with your build!