Intel i5-3570K Ivy Bridge 3.4GHz (add an aftermarket cooler if you decide to OC)
ASRock Z77 Extreme4 HDMI USB 3.0
Crucial Ballistix Sport 8GB DDR3 1600
Seasonic 620W 80 PLUS BRONZE Certified
EVGA GeForce GTX 670 4GB 256-bit GDDR5
1TB Hard Drive 7200 RPM
Rosewill THOR V2 Gaming Full Tower w/ 4 case fans
i usually shy away from SLI/Xfire on a new build... just get the biggest card you can afford and the MOBO will allow you to add a 2nd GPU in the future if you choose to. A single GTX 670 4GB graphics card (included in this build) will handle just about everything you throw at it.
this pc can be had for around $1200 (not including OS)...adding a 120GB SSD as your system drive is something to consider too...just add about $100 to the total
Gone are the days that you need giant motherboards with massive cooling for your CPU to get good gaming. You can get good gaming off of an i5 on an Mini ITX MoBo.
The key to gaming machines is the GPU. I am kinda a GeForce fan boy so I recommend an MSI 660ti power addition. Seems to me to be the best bang for the buck.
Memory - 8 Gigs or more. I like Corsair or Crucial.
PSU - Any thing that is 80+ Gold or better and like 900 Watts or more.
HDD - One 250 GB Intel SSD or if you have the money 2 in Raid 0. Also one 2 TB Western Digital for data.
OS - Windows 7 (Don't like 8 because of Metro) just because there are more games for Windows but OSx and Linux are nice too.
CPU Cooler - Corsair H80i