Some of my faves:
xpat2 - best card games app - unstable feed
rockdodger - shootemup - anuakins feed
defendguin - defender clone - shmigols feed
xmahjongg - puzzle type game - cortez feed
gweled - puzzle - anuakins feed
xboard - chess - jabbaths feed
There is xgalaga but it doesn' fit the screen very well so i won't recommend it.
IMO these games would be a nice for a "base" install if that is what you are after