Of the only 30 or so games from the '70s, Combat, Air-Sea Battle, Basketball, Home Run, and Bowling are the only ones that screamed Atari for me and were ones I ever replayed. Breakout and Indy 500 would be on this list if I had them back in the day.
But truth be told, if it weren't for the next series of games, I would have gotten bored and rather played outside. So some more games that defined the Atari for me and more importantly hooked me into video games were (in approximate order of publication according to Wikipedia):
Space Invaders (1980) [Defined the Atari--all my friends loved it--, but it's one I hate with a passion to this day], Asteroids (1981), Missile Command (1981), Haunted House (1982), Pac-Man (1982), Yars' Revenge (1982), Chopper Command (1982), SW: The Empire Strikes Back (1982), Defender (1982), and Star Raiders (1982). I went more than ten, because I loved that with Defender I didn't have to hit a button to change direction, and I never found anything like Star Raiders (or Haunted House for that matter) in the arcades that I remember.
Both Warlords (1981) and Berzerk (1982) would have been my Ur-games for Atari if I had them back then. It pisses me off to this day that I never saw these.