700-900$ gaming build

Here you go..
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD FX-8320 3.5GHz 8-Core Processor ($153.83 @ Amazon)
CPU Cooler: Thermalright Macho-120 73.6 CFM CPU Cooler ($43.98 @ SuperBiiz)
Motherboard: Asus M5A99FX PRO R2.0 ATX AM3+ Motherboard ($126.98 @ SuperBiiz)
Memory: A-Data XPG V2 8GB (2 x 4GB) DDR3-1600 Memory ($69.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($59.98 @ OutletPC)
Video Card: Gigabyte Radeon R9 270X 2GB Video Card ($249.98 @ SuperBiiz)
Case: Rosewill CHALLENGER ATX Mid Tower Case ($45.24 @ Amazon)
Power Supply: EVGA SuperNOVA NEX750B BRONZE 750W 80+ Bronze Certified Semi-Modular ATX Power Supply ($59.99 @ NCIX US)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($16.98 @ OutletPC)
Total: $826.95
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-02-13 19:02 EST-0500)

Better video card is good buy so try to fit this in your budget.
http://pcpartpicker.com/part/gigabyte-video-card-gvr928xoc3gd

Or intel build.
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($219.99 @ Amazon)
CPU Cooler: Thermalright Macho-120 73.6 CFM CPU Cooler ($43.98 @ SuperBiiz)
Motherboard: Gigabyte GA-Z87-HD3 ATX LGA1150 Motherboard ($109.99 @ Newegg)
Memory: A-Data XPG V2 8GB (2 x 4GB) DDR3-1600 Memory ($69.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($64.99 @ Newegg)
Video Card: Gigabyte Radeon R9 270X 2GB Video Card ($249.98 @ SuperBiiz)
Case: Rosewill CHALLENGER ATX Mid Tower Case ($45.24 @ Amazon)
Power Supply: EVGA SuperNOVA NEX750B BRONZE 750W 80+ Bronze Certified Semi-Modular ATX Power Supply ($59.99 @ NCIX US)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($16.98 @ OutletPC)
Total: $866.13
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-02-13 19:06 EST-0500)

Cheap 128GB SDD makes your programs ru nreally fast so that is good to have in new build.
http://pcpartpicker.com/part/sandisk-internal-hard-drive-sdssdhp128gg25
 
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