If gaming is your main concern, I would also recommend a sound card, like a xonar or x-fi. If it's not in the budget now, you can easily add it later. Assuming you have good speakers, it can really improve your gaming experience.
The Cooler Master ATCS 840 is also in your price range if you want a really nice, no-frills, feature-rich case. It has some really slick usability perks (namely full removable ball-bearing track mobo tray) and the large 240mm fans, but more noise may escape than in the Cosmos if you have something really loud inside (namely a video card with a fan running at mach speeds).
I'm having trouble deciding on the GPU. I don't know why I didn't think of picking a silent GPU beforehand until rescawen mentioned the 4890 vapor-x. I should mention that I don't mind spending the extra money for a better card combination since I'm still within my budget. The total cost of the new PC right now is floating between $1600-$1700 depending on the video card choice. I've taken your suggestion on SLI/X-fire over a single expensive GPU.
right now I'm torn between the following video card choices:
I was reading that the EVGA 260 GTX card has reasonable noise levels on the fan as well. Do you think there would be a major difference between the noise levels of these two cards? I would also be willing to pay a bit more for increased stability / lower temperatures. If anyone has other video card configuration suggestions I'm up for those as well.