Gamestop has a new promotion where they will give you an extra $50 trade credit when you trade in your Xbox One and PS4. The trade value for an Xbox One is typically $100 and for the PS4 is $125, both for 500GB systems before the extra $50 credit.
If you have a bigger hard drive system then the prices will be slightly different. The deal is only good for credit and not cash. The offer expires on February 12.