This is one of the tip-ins when I was considering buying an iBook: Solarian II.
This was an awesome game on the Mac II back in the early 1990s, and it's just as addictive in its current incarnation as it was back then. It's a variation on Space Invaders or Galaga, only with some really cool sound effects (which I'll record and post in the future).
Click on the picture for a larger view.