New CPU/Motherboard

I am building a new computer and i have everything selected except a motherboard and CPU. The graphic card i will be getting is the EVGA GTX 680 so i need a CPU that will pair well with this playing games and streaming at a resolution of 1920x1080 without bottle necking to much if possible. I had an idea of what i wanted although i do not want to make a mistake when it comes to spending a this much money. I am transferring my drives (HDD, SDD, CD) from my old computer so i am upgrading everything else. any help would be appreciated.

What i have selected:

RAM: G.SKILL Sniper Series 16GB (2 x 8GB) 240-Pin DDR3 SDRAM DDR3 1866 (PC3 14900)
Cooling: CORSAIR Hydro Series H100i Water Cooler
Case: COOLER MASTER HAF 932 Advanced RC-932-KKN5-GP Black Steel ATX Full Tower Computer Case
Power Supply: CORSAIR HX Series HX850 850W ATX12V 2.3 / EPS12V 2.91 SLI Ready CrossFire Ready 80 PLUS GOLD Certified
Graphic Card: EVGA 02G-P4-2680-KR GeForce GTX 680 2GB 256-bit GDDR5
Motherboard: ???
Processor: ???

My budget being spent between the motherboard and CPU is around $400, no more then $500.