You really aren't going to find any games if you don't install podzilla or some variant of it. If you aren't willing to do that, the closest thing to add on games you will be able to find are ones that are basically text based games, which use Notes and links inside the notes to navigate the game(Such as the ones found
here at ipodarcade.com.
Course you might want to give podzilla a try, the basic podzilla at ipodlinux.com offers the ability to play alot more games,asteroids, chess, lights, othello.. etc..., I even have DOOM on mine, though it looks a bit off since its in black and white on my 3G iPod.