What resolution are you going to be gaming at, 1080p or something else?
Are you gonna build it or do you want a prefab one?
Probably gonna want to get a nvidia 970 if you're at 1080p (about $350 or a third of your budget), to be more future proof. Right now you only need an i5, but that may change in the future, with new games recommending an i7 and directx 12 coming out, which will use more cores. It's up to you about how future proof you wanna be. I guess you really only need 8gb of ram (but I'd personally go for more, but that's just me). You can get a cheap case for $100 dollars or some shyt. You don't have to go all out on the motherboard unless you want to. Try to get a 250gb ssd, but it's not a necessity (highly recommended though). Probably can get a fairly good psu for under $100 if you look.
This seems like a good build, just change out the video card to the latest (the nvidia 970) (and add a bigger ssd or change the case for whatever you want).
http://www.tomshardware.com/answers/id-1971551/1000-gaming-build-2014.html
CPU:
Intel Core i5-4670K 3.4GHz Quad-Core Processor ($233.99 @ SuperBiiz)
CPU Cooler:
Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($33.98 @ SuperBiiz)
Motherboard:
Asus Z87-A ATX LGA1150 Motherboard ($129.99 @ Amazon)
Memory:
G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory ($69.99 @ Newegg)
Storage:
Kingston SSDNow V300 Series 120GB 2.5" Solid State Disk ($69.99 @ Amazon)
Storage:
Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($58.98 @ OutletPC)
Video Card:
Sapphire Radeon R9 280X 3GB Video Card ($349.98 @ NCIX US)
Case:
Fractal Design Define R4 w/Window (Titanium Grey) ATX Mid Tower Case ($82.99 @ NCIX US)
Power Supply:
Corsair Gaming 700W 80+ Bronze Certified ATX Power Supply ($79.99 @ Microcenter)
Optical Drive:
Asus DVD-E818AAT/BLK/B/GEN DVD/CD Drive ($18.98 @ OutletPC)
Total: $1121.87
If you don't wanna build it yourself, you can pick all your parts and have these people build it for you
http://www.cyberpowerpc.com/
They have a ton of builds too