well those games really arent graphically demanding you could go with this
PCPartPicker part list:
http://pcpartpicker.com/p/3e2PX
Price breakdown by merchant: http://pcpartpicker.com/p/3e2PX/by_merchant/
Benchmarks: http://pcpartpicker.com/p/3e2PX/benchmarks/
Video Card: EVGA GeForce GTX 750 Ti 2GB Video Card ($159.99 @ Best Buy)
Power Supply: Antec 450W ATX Power Supply ($29.99 @ Newegg)
Total: $189.98
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-03-21 20:21 EDT-0400)
here is the benchmarks for it
http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_750_Ti/16.html
honestly the 750 ti could probably run on your current psu but i would recommend upgrading it just to be safe
if you want something that will do well in newer games (bf4, titanfall, etc) you could go with this
PCPartPicker part list:
http://pcpartpicker.com/p/22GUb
Price breakdown by merchant: http://pcpartpicker.com/p/22GUb/by_merchant/
Benchmarks: http://pcpartpicker.com/p/22GUb/benchmarks/
Video Card: Gigabyte Radeon R9 270X 2GB Video Card ($229.99 @ NCIX US)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($59.99 @ Newegg)
Total: $289.98
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-03-21 20:25 EDT-0400)
but if your just playing skyrim and d3 at 1080p the 750 ti should max those games