I echo the above sentiments. These are my "must have" games:
Centipede
Millipede
Marble Madness
Crystal Castles
plus my new favorites:
Shuuz
Shuffleshot
Beyond that, it's just a "wow" factor. I actually have swappable panels, and keep the same dimensions as the old classic cabinet I have them in. People see my arcade cabinet, and they say "too bad you can't play games like millipede". I pull out my trackball, and they say "wow - it's just like a real arcade". Of course, the joystick and buttons are just like an arcade, but people have SEEN those before at least in replica form with those "arcade style" sticks for the consoles. An honest-to-goodness arcade trackball is unique in a home environment.