You won’t want to break your bank balance on a gift for a gamer nor get something they probably already have, that leaves some of the cool extra PC gaming accessories:
The Razer Tartarus V2 Gaming Keypad, if they’re into MMOs
The Elgato Stream Deck if they’re into ‘Twitch’ streaming
Any of the wheels or flight accessories which you could purchase with the games if they don’t already have them
The Razer Base Station if they have the headset
Or, any of the gaming mats/surfaces make for a good gaming gear gift