If it really needs to be under $800,
PCPartPicker part list:
http://pcpartpicker.com/p/3JGMk
Price breakdown by merchant: http://pcpartpicker.com/p/3JGMk/by_merchant/
Benchmarks: http://pcpartpicker.com/p/3JGMk/benchmarks/
CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($189.99 @ NCIX US)
Motherboard: MSI B85M-P33 Micro ATX LGA1150 Motherboard ($58.98 @ SuperBiiz)
Memory: A-Data XPG V1.0 8GB (2 x 4GB) DDR3-1600 Memory ($63.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($54.43 @ OutletPC)
Video Card: Asus GeForce GTX 760 2GB DirectCU II Video Card ($239.99 @ Newegg)
Case: Cougar Solution (Black) ATX Mid Tower Case ($37.99 @ Mwave)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply ($34.99 @ NCIX US)
Monitor: AOC E2260SWDN 60Hz 21.5" Monitor ($99.99 @ Newegg)
Keyboard: Gigabyte GK-KM6150 Wired Standard Keyboard w/Optical Mouse ($18.99 @ Amazon)
Total: $799.34
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-05-14 01:29 EDT-0400)
I dropped the disc drive completely. You can always add one later at any time.