Easy: GTX 750 Ti.
Decent card, will run most intensive games on medium settings with acceptable frame rates, doesn't require a good PSU and falls right in your budget.PCPartPicker part list
/ Price breakdown by merchantVideo Card: EVGA GeForce GTX 750 Ti 2GB Superclocked Video Card
($99.99 @ Newegg) Total:
$99.99Prices include shipping, taxes, and discounts when availableGenerated by PCPartPicker 2015-11-19 04:09 EST-0500