Heres a Acer Aspire with a i5 & 840M 2gb GPU for $639.00 although its not out until 2/6/15:
http://www.newegg.com/Product/Product.aspx?Item=N82E16834314807
The headset/mouse is more of a personal preference but I'd go with a Turtle Beach headset and for the mouse either Logitech or EVGA is good.
For $650 you could build a significantly better desktop. I built this on PCPartpicker for a bit over $650 and would be faster then that I5. Also I5 mobile chips are only dual cores with quad threads (similar to I3 desktop chips).
PCPartPicker part list:
http://pcpartpicker.com/p/fR6nCJ
Price breakdown by merchant: http://pcpartpicker.com/p/fR6nCJ/by_merchant/
CPU: Intel Core i3-4160 3.6GHz Dual-Core Processor ($109.99 @ NCIX US)
Motherboard: ASRock H97 PRO4 ATX LGA1150 Motherboard ($83.99 @ SuperBiiz)
Memory: G.Skill Sniper Series 8GB (2 x 4GB) DDR3-1600 Memory ($74.98 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($48.88 @ OutletPC)
Video Card: EVGA GeForce GTX 750 Ti 2GB FTW ACX Video Card ($131.99 @ NCIX US)
Case: Azza SIRIUS ATX Mid Tower Case ($29.99 @ Newegg)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply ($39.99 @ Micro Center)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($13.98 @ OutletPC)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($88.98 @ OutletPC)
Case Fan: Aerocool Shark 82.6 CFM 120mm Fan ($10.99 @ Directron)
Case Fan: Aerocool Shark 82.6 CFM 120mm Fan ($10.99 @ Directron)
Keyboard: Cooler Master CM Storm Devastator Gaming Bundle Wired Gaming Keyboard w/Optical Mouse ($27.99 @ NCIX US)
Total: $672.74
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-02-02 10:20 EST-0500