http://nokia-n900.com/nokia-n900-maemo-game-galaga/

Credits go to the original poster for uncovering Galaga.

For whatever reason, these Namco games are only available in Malaysia-Singapore region. You have to browse through proxy to install them. (I am not sure if it's legal to distribute .install files)

Both games are free and of very good quality. Galaga is touch-controlled only. To me, the single-touch limitation of N900 takes away some fun factor. Pacman is also touch-controlled, but the control makes better sense here and the game is really fun to play.