I assume the only reason no-one wants Unity of Command keys is because it is an extremely Cool and Good game that everyone owns already.
More keys for a bunch of smaller games:
Warhammer 40,000: Regicide
Human: Fall Flat
SEUM: Speedrunners from Hell
Stronghold Legends: Steam Edition
Zombo Buster Rising
Green Game: TimeSwapper
Home is Where One Starts...
Chicken Assassin - Master of Humiliation
The Battle for Sector 219
Global Soccer Manager
Axis Football 2016 (I was disappointed this is NOT a game about Germany playing soccer against Italy in some weird alternate timeline where the Nazis won)