Centipede! I even went so far as to buy a table top bar model :P The 1st player side broke and it was heavy as crap, so I gave it away - but at the GameWorks party in Vegas, you'll always find me at the Centipede machine.
I also like Galaga for standing/sitting video, Tetris for handheld and there was some bunny game that was a hoot for Super Nintendo or PS that was really fun
