Here are two suggested builds, with all the common components first. Prices from newegg.com
GPU: XFX HD-697A-CNFC Radeon HD 6970 2GB - $330 after rebate
PSU: CORSAIR Enthusiast Series TX850 V2 - $125 after rebate
Case: COOLER MASTER HAF 922 - $95 (I chose a popular case, there are plenty of other good options to choose from, take your pick)
CPU Cooler: COOLER MASTER Hyper 212 Plus - $25
HDD: Seagate Barracuda 7200.12 ST3500413AS 500GB - $55
Optical: DVD burner, take your pick - $20
Memory: 2x4GB DDR3-1600 CL9 1.5V, take your pick - $35 after rebate (current cheapest price)
The corsair is a quality PSU and you'll need 60A on the 12V to power those cards and overclock the processor. Each 6970 takes 250W max (or 21A each) and the processor could take 10-12A depending on which you chose and how much you overclock (no reason to get an i5-2500k and not overclock). Throw in peripherals, HDDs, and so forth and you are getting up there. You might be able to find another quality PSU for slightly cheaper, but I didn't feel like searching too much.
8GB ram is enough for any gaming build, and $35 is a good price. CPU cooler is needed for overclocking and this one is good for simple overclocks. If you want to go crazy get something better. The GPU is the one you chose.
Sub-total: $685
Intel:
CPU: i5-2500k - $220
Motherboard: ASRock Extreme4 Gen3 Z68 - $200 after rebate (P67 version is $160)
Total: $1105
ASRock Extreme4 Gen3 is very "future proof" capable of supporting SLI/Crossfire, Sandy Bridge, PCIe 3.0, USB 3.0 and overclocking.
AMD:
CPU: AMD Phenom II X4 955 - 980, You can overclock a 955 to 980 levels, so pick whatever you want - $120-170
Motherboard: ASUS M5A99X EVO AM3+ AMD 990X - $150
Total: $955-1005
The ASUS board has pretty much everything you can get out of an AMD board. You can get more of everything with more expensive boards, but this one is good for overclocking and not a bank breaker. I'd also probably get the 955 and overclock it. I might not get as fast as I would have with a 980, but I should at least be able to get to 980 stock speed.
Still Needed:
OS - $100 for Win 7 Home OEM
Peripherals - $x whatever you decide to spend
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If I were to choose between the two, I'd probably go Intel, however with the $150 saved you could buy a SSD with the AMD build. However (again), with that said, you can buy an ASRock Extreme3 Gen3 for the Intel build and save $75 and buy an SSD with that money.