What were hands down the best games on the Atari 2600?
My favorites:
Missile Command
Space Invaders
Yars’ Revenge
Dodge 'Em
Others made by third-party companies:
Megamania (Activision)
Frogger (Parker Brothers)
Demon Attack (Imagic)
Cosmic Arc (Imagic)
My Favorites:
Yar’s Revenge
River Raid
Keystone Cops and Robbers
Midnight Magic (arrived pretty late in the 2600 lifespan, but it had nice graphics and was pretty good pinball game)
Pitfall 1 and 2
I have to second River Raid, Yar’s Revenge, and the Pitfalls.
I liked Combat and River Raid the best because I kicked serious ass on both.
That was, btw, the last video game platform I’ve owned.
I loves me some Elevator Action.
Pitfall was the bomb! I also played the hell out of Yar’s Revenge, Asteroids, Space Invaders, Missle Command, and Super Breakout.
My 2600 is at my Mom’s house, and last I checked it still worked. Maybe when I’m home for Thanksgiving I’ll bring it back with me.
My favorite 2600 game was Adventure. One of the pioneer maze-puzzle type of games.
Actually, my favorite system was the 5200. If only the controls didn’t suck and break in minutes. But the games rocked!
The 7800 was a decent system, but by the time it rolled out, Atari was into its “get the hardware out but don’t make any games” mode.
When the Lynx came out I was positive it would kick GameBoy’s butt. Again, no software = no sales of hardware.
Decathalon, for the sheer joystick-breaking fun of it.
Adventure
Haunted House
Maze Craze
Chopper Command
Robot Tank
Dolphin
Frostbite
MASH
Astroblast
Frogs n’ Flies
Oink
Kaboom!
The list goes on; the 2600 is the only console I still own, along with a laundry basket full of about 150-200 games.
…but really, nothing can surpass the classic:
While we’re on the subject, does anyone know if Chuck Norris Superkicks can be beaten? I could get to the black belt area no problem, but I could never kill enough ninjas before the time ran out.
Joust
River Raid
Pitfall
Yars’ Revenge
H.E.R.O
H.E.R.O.
I loved the little helicopter backpack, and the way you had to light dynamite and then fly away before it detonated.
Berserk
Once I mastered the art of firing off the screen at an angle to hit the robots on the other side of the screen, I played endlessly one weekend, had something like 30 billion points, and turned it off.
Decathlon
This holds a special place in my heart, as my older brothers didn’t realize that you could hold down the “turbo” button on our new joysticks, (after we broke the old ones playing this game), so I pretended to be moving back and forth, and not only beat them every time, but won a World Record every time. Yeah, I got my ass kicked when they figured it out, but it was worth it. 
Pitfall
My goal after getting bored with winning everything was to jump over some treasure, enter the next screen and jump on the rope, then immediately jump back off and run to the left and pick up the treasure. The goal was to get the Tarzan sound byte to get cut off by the Treasure sound byte. I’m a loser.
Megamania - which is available on the Activision PS2 game also. I was better at it.
Adventure also, which was simple but oddly compelling - especially when you found an early Easter Egg in the game.
Mattel publshed an Empire Strikes Back game, where you flew a cruiser shooting at walkers. They got faster and faster.
I got the secret on Pinball, and wrapped the score three times every so often.
Also
Asteroids
Space Invaders
Frogger
Stampede
Circus
Bridge
and not PacMan!
Am I the only person who liked that skydiving game?
Ms. Pac-man was a great cartridge.
H.E.R.O
Pitfall II
River Raid
The M-network Tron games(hey, they came with this giant glowy blue trigger style controller).
Kaboom!
Forgot:
Yar’s
Phoenix. I loved this cartridge. You could make it crash by flipping the power on and off real quick, giving you infinite lives.
Decatholon, except for what it did to my hands.
As already repeatedly stated:
H.E.R.O
and
Pitfall II
Activision owned the 2600 games.
And now Atari is beating them in the home computer market.
Megamania
Pitfall
Yar’s Revenge
In my dotage I have developed a new appreciation for Adventure and often play a game before I go to bed.
–Cliffy
As mentioned, Chopper Command. My brother and I thought we were really cool, because we sent in pictures of our scores (I think it had to be 100,000 or better) and received patches.
I also had a lot of fun playing Moonpatrol, but never did beat the game.