with $2500 budget... if i were you... i can even buy almost the best component available in the market... but i won't be doing so... just take a look...
cpu:
http://www.amazon.com/Intel-BOX80623I52500K-Core-i5-250...
Intel Core i5-2500K - $225
verdict: since you maybe overclocking... the k-series cpu comes in handy for the purpose... while your budget allows you to stretch to x79 build... for the moment i still don't see the reason to pay much more for that since your main purpose is gaming while sandy bridge is more than enough to do the job.... as for picking i5-2500k over the i7-2600k again.... based on your need... the latter seems provides not enough justification for you to pay extra $100 again just for gaming...
mobo:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
ASRock Z68 EXTREME4 GEN3 - $185
verdict: i think this board has the best feature you can get while not spending too much on it... as for what this board has over the competition you can visit this page...
http://www.asrock.com/mb/overview.asp?Model=Z68%20Extre...
one more thing... unless you're looking for the best overclocking motherboard(it's not that you're ever going to oc the hell out of it since it'll shorten your system lifespan) this board has almost everything you need for the price...
psu:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
OCZ ZX Series 1000W Fully-Modular 80PLUS Gold - $180 after MIR
verdict: corsair ax1200 is certainly one of the best psu you can buy... but the question is... other than seasonic and corsair... is it really no other brands out there worth considering? well... i'm certainly one of those who don't think so... for the price... this 1kw model offers pretty much everything you need for less money... that 1.2kw psu is for those people who runs three graphics card setup and hard overclocking their systems... once again i know your money is more than enough to spend for it... but sometimes you don't really need to spend that much to get something that satisfies you...
ram:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
G.SKILL Sniper Low Voltage Series 8GB Model F3-12800CL9D-8GBSR2 - $50
verdict: ram has less impact on gaming performance... so usually most 8gb kit that runs at 1600mhz cas 9 will be enough to do the job... but from what i've seen... there is a trend of using a lower voltage ram while switching from previous gen platform to the another... so i choose one of the lowest voltage kit available in the newegg store....
hsf:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
CORSAIR CAFA70 - $19 after MIR
verdict: a sub 20 dollars for a cooler that do its job well... so any reason pass on this one? certainly yes... if you're going to overclock your cpu like hell... otherwise this cooler is up for the selection...
ssd:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Plextor PX-M2P Series PX-128M2P 2.5" 128GB - $250
verdict: while this particular model is not the fastest... or the cheaper ones... it certainly is one of the most stable controller among the ssd market... and since a $2++ is a hefty amount to pay for a 128gb capacity ssd... so really need to choose carefully... mind you... there are cheaper ones on the market... but this one still gets my vote...
case:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Antec Eleven Hundred - $130
verdict: it's been hard to find a case that can accomodate large components... have great coolings while not being overly designed on its looks... while i would really like to recommend a silverstone fortress ft02... because i like it so much for its look and performance... its price that eventually makes me putting it aside for alternative... antec recently release a new eleven hundred... it has many options for adding fans... while retaining its simple looks compared to the competition... only its downside i can say is... if you're eventually stepping into a water cooling... diy based loops... i suggest you looking for another model as this case certainly need some modding if you want to install water cooling components...
hdd:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
SAMSUNG Spinpoint F3 HD103SJ 1TB - $150
verdict: add some more cash... and you'll get another 500gb... so why not?
gpu: this is the last and the most important part in whole build... while building a crossfire setup with 2x hd 6950 seems like awesome... i had to mind you that.... as early as Q1 2012... amd will be releasing its next gen hd 7900 series... and soon followed by nvidia... and it's just a few months away... buying 2 cards at this time seems like not a good idea as $600 isn't a small amount of money you know... but if you wait a little more... and you can get next gen series card which will eventually faster than this gen card... and will last you even longer before your next upgrade... even if these new cards will costs you more i assuming that each card costs $500 for hd 7970 for example... at least your budget still allows you to stretch that further... so my advice will be... put on hold your desire to purchase in this area and use your cpu's built-in graphics and wait for couple of months... and you eventually will be very satisfied by the time you holding two next-gen cards...
total spending all of these parts listed above - $1189 after MIR excluding shipping
okay... enough with over-typing... i hope my advice does help you in your build...