well if you have a Nintendo DS, GBA SP, normal GBA, or a GBA micro, you can buy copies of all your classics on GBA. (gameboy advance). their are websites where you can download trials of these games. just go and type in something like dos games because i believe they can run in dos.
here is my ALL time favorite, never can be beat, ultimate game.
but for others i like pacman, space invaders, asteroids, and yea that's about it.
if you interested in some new old school style games check out this game.
take asteroids, kick up the speed by like 10, add 50million enemies and turn the graphics to ultimate and you got geometry wars.