you have some of the better titles. get UFO (challenger series). some of the original releases had some interesting quirky titles , thunderball (pinball like), invaders from hyperspace, and a few sports games i am pretty fond of like alpine skiing and volleyball. And of course the master strategy series games, keep in mind that most of those early O2 games are best played with a 2nd player.
Although frogger and qbert are titles worth getting, i wont suggest them only because they are not likely to be had as easily and as cheap as the former games.
cheers
lee