for that price range im not sure why most people are recommending amd, you could spend a bit more and go intel (both are good, I prefer intel)
You can always SLi later down the road but on a 1920x1080 screen the GPU below should pretty much max out almost all games you throw out it. You can check out either of my builds which would basically be the same build give or take the companies used. After building over a dozen computers in the past two months- trust me on this spend a bit more for the higher end stuff because it will last you longer and give you less problems. this build will be pretty much future proof for the most part, all you will need to add if you want to play games maxed out in a few years would be another 660 to SLI or just sell it and get a new one..
motherboard 1155 socket- ~100-200$
16gigs ram- ripjaw ~$100
gpu- 660gtx ~200-250 EDIT: 7970 is a great gpu too if you want to spend a bit more
psu- hx/ax 650-750w ~$100-150
computer case (whichever you like) will be around $100-160
SSD 128 gigs~ (i recommend samsung or crucial~ $100
WD caviar black hard drive ~$100
you can get any type of cpu cooler, water or air is preference the only difference is a few degrees so if your not too much of a perfectionist both are basically equal. some nice ones are the corsair H series, antec 920 those are both water- for air you have the nocturna and many more, just check reviews.
that should be about $1150-1250
you should have enough to get yourself a nice monitor, and any other accessories, if you have any questions feel free to ask!
benchmarks of the amd 8350 vs the 3770k cpu i recommended : http://teksyndicate.com/videos/amd-fx-8350-vs-intel-3570k-vs-3770k-vs-3820-gaming-and-xsplit-streaming-benchmarks