Cannot really recommend Asrock boards. An ASUS or Gigabyte z68 board would be a better choice. Low or high end does not matter. Quality is just as good. USB 3.0 ports on the case is going to require same headers on the motherboard which will drive up the cost a bit.
8gb DDR3 1600 ram kit(2x4gb) would be just as good and optimal for Win 7 64 bit. The 3,6,12gb kits were really made for the old 1366 series Intel boards. Also, that tall Corsair ram will likely interfere with the cooler, and is really made just for looks. Best to stay with the lower profile stuff from Kingston, Corsair and Gskill.
PSU depends on card(s), but a 750-850 watt 80 plus bronze certified from Antec, Corsair, Seasonic, Silverstone, or XFX is preferred. Newegg has good prices right now. I would also check them on the other items except for processor.
Cases with USB 3.0 ports are a bit more expensive just like the motherboards that would support them. The Coolermaster HAF series, the Antec 300, CM 690, and similar mid to full towers from other makers are the most popular right now. Generally in the $50 to $70 range.
For your heatsink: the tuniqu 120 extreme is the best performing heatsink for the money/noise. it is the quietest heatsink in the top 5 intel heatsinks.
also for RAM i like the GeIL Enhance CORSA 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600. it is tested at 1700 speeds for extra stability! and only ~ $42
Case: im partial to the Antec Three Hundred. ~ $60 it has great airflow. however if you want something a little bigger go with a COOLER MASTER Storm Scout ~ $90
GPU: http://www.newegg.com/Product/Product.aspx?Item=N82E168... 7970 is THE BEST singe GPU VGA card out there better than the 580 in almost all games (if not all). it overclocks amazingly and can play every game at MAX settings 60+ FPS average. also down the road you can get a second one and since AMD's multi gpu scaling is near 100% you will almost instantly double your gaming capability for in 2-3 years when you might need a new card. These cards are a little pricey but perform twice as fast as a 6950 which is over half the price. deffinately worth the extra money since its a single card and WILL give you the performance you want for todays games.
PSU: Thermaltake TR2 RX 750W Bronze ~ $90 cheap efficient and enough headroom for a second 7970 down the road. its also modular so that you will get better airflow in your case.
the 7970 may push you a little over but the gains are perportional so i see it as worth it down the road.
And personally i think there is nothing wrong with ASUSROCK but the xtreme3 gen3 is cheaper and i think a better value.