There's a space invaders cocktail one that has you playing at the same time and your shots can kill each other.
You can also play sprint and super sprint if you leave the orientation of the screen facing the long way.
Don't forget, you can do the same with Gauntlet, jsut remap the controls so that they relfect the way the character moves in the game from your perspective. (And leave the game running horizontal.)
Smack