There is an old school top-down shooter you can unlock in Call of Duty: Black Ops for the PS3, Xbox 360, and PC called Dead Ops Arcade.
To unlock Dead Ops Arcade, you need to access the computer on the main menu. To access the computer, you need to mash the aim and shoot buttons (on PC, just mash the spacebar) until you break free of your restraints. Once you break free, walk up to one of the computers behind you and type in DOA to unlock Dead Ops Arcade.
Alternatively, you can type in 3ARC UNLOCK to unlock both Dead Ops Arcade, and Presidential Zombie Mode.
