It makes it easier for us to simply read though your requirements and then choose parts according to your overclocking/multiGPU/Budgetary/etc wishes!
Some initial advice though!
Generally for gaming computers you don't want to go for anything over 4 cores. The extra cores are simply not utilized in modern games and you have the issue of a quad core CPU is faster than a Hexa core CPU with 2 of the cores disabled! In the AMD Range the Phenom II x4 955 or 965 are optimal for this use!
For the motherboard I tend to recommend the 800 series chipset from AMD and for the moment the ASUS range of motherboards as they are supposed to be offering Bulldozer support via a BIOS update which would allow upgrading to the AMD FX series without having to buy a new motherboard, and then OS
For other parts just quickly (you can find all these on newegg but I do not have time to post links I'm sorry)
CPU -- AMD Phenom II x4 955 B.E.
RAM -- GSKILL Ripjaws 8GB 2 by 4GB sticks
MOTHERBOARD -- http://www.newegg.com/Product/Product.aspx?Item=N82E16813131631
GPU -- ASUS AMD Radeon 6950 Direct CUII edition
CASE -- Cooler Master HAF 912 or similar (Case preferences please)
Power Supply -- Seasonic M12 620 watt or larger if wanting to crossfire later!
OS -- windows 7 Home Premium
Yep thats the one! Generally with the Radeon GPUs you'll want to get one with a different cooler to the stock edition! The stock edition uses the centrifugal fan which gets quite noisy! The Radeon GPUs however are better if you are going with an AMD processor as they don't require as much CPU power to run!
Please take a quick look at the latest intel Sandy Bridge range of CPUs aswell before you make a decision on the build! I'd be recommending the Core i5 2500 edition for about $200 and a P8P67 motherboard from ASUS! I assume that you would rather not overclock your CPU?