That's asking for a crap-shoot of suggestions. The reality is, a monster gaming PC including the works can be built for $1.5K - $2K. It eventually gets to the point where you begin seeing diminishing returns with the higher budget and more expensive parts. PCs that cost something insane like $5K is just overpriced and overkill. Within one or two year's time, newer stuff will be out that performs the same and more efficiently, yet cost less. And of course there will be faster stuff that fills in the high budget sector again. This is why it doesn't make sense to spend oodles of money on one machine at one point of time. If you're seriously into PC gaming, upgrading pretty much becomes common practice.
So even if I had an unlimited amount of money, I actually might end up building multiple PCs. Then again, I'm always looking for deals...I'm not rich. If I was to indulge though...
CASE: http://www.newegg.com/Product/Product.aspx?Item=N82E16811139001
CPU+MOBO: http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.324969
RAM: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231247
HDD1: http://www.newegg.com/Product/Product.aspx?Item=N82E16822136456
HDD2: http://www.newegg.com/Product/Product.aspx?Item=N82E16822136284
PSU: http://www.newegg.com/Product/Product.aspx?Item=N82E16817139010
GPU: http://www.newegg.com/Product/Product.aspx?Item=N82E16814102863&cm_re=radeon_5970%2d%5f%2d14-102-863%2d%5f%2dProduct
DVD: http://www.newegg.com/Product/Product.aspx?Item=N82E16827136181
HSF: http://www.newegg.com/Product/Product.aspx?Item=N82E16835608018
OS: http://www.newegg.com/Product/Product.aspx?Item=N82E16832116758
SOUNDCARD: http://www.newegg.com/Product/Product.aspx?Item=N82E16829271004...or...http://www.newegg.com/Product/Product.aspx?Item=N82E16829156005
SPEAKERS: http://www.xoxide.com/logitech-z5500-surround-speakers.html
MOUSE: http://www.newegg.com/Product/Product.aspx?Item=N82E16826104318
KB:http://www.newegg.com/Product/Product.aspx?Item=N82E16823126034
LCD: http://www.newegg.com/Product/Product.aspx?Item=N82E16889005064...or...http://www.amazon.com/gp/product/B001VKYAKO/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B001VKYAL8&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1VA2SZGKE95HEK354531...quick repsonse time S-IPS panels.
Probably under $4K for all that. A single Radeon 5970 would max everything under the sun at 1920x1080 resolution, so don't see much point in getting another for quadfire. Again...diminishing returns.
If I had unlimited money to buy a computer, I'd definitely get one of http://www.artlebedev.com/everything/optimus/.

Because it's not overkill at all!
Alright, now for a serious question. Recently my hard drive has started making noises. They aren't loud, just a faint little scratch or ticking noise, like a needle against metal. I feel like this is a sign of my hard drive failing, would I be right in that? Is there some way to test it to see if it's failing or am I just going to have to wait for it to bite the dust? I have all my important files backed up to an external drive already, luckily.