This my personal Best of 2600 list.
Some of these games are part of my list because I grew up playing them, others are just there because they are classics but the vast majority are there because they are actually still fun to play today. I tried not to put many arcade ports on here but there is a couple if they were actually really good ports. There are a couple of improvement hacked roms which are homebrews and not hacks that you would need to get and they are freely available over on http://atariage.com/index.php they are not copyright protected so there is no worry about that.
Space Rocks thread and download http://atariage.com/forums/topic/197315-space-rocks-2600
Pac-Man (8K) post and download http://atariage.com/forums/topic/229152-new-pacman-for-atari-2600/page-37#entry3298369
Here is the list of games in the playlist file and a short blurb about it:
Adventure - Not really a favourite of mine but it is a classic 2600 game.
Atlantis - Sort a Missile Command clone but different enough and unique.
Barnstorming - Fly through barns, what other games offer this ?
Beamrider - Another game that isn't really a favourite of mine but many people like it so it's here.
Berzerk - Arcade port but really well done.
Boxing (Activision) - This game is a great 2 player vs game, really fun button mashing action.
Chopper Command - Horizontal shooter Defender clone but by Activision so you know it's good.
Communist Mutants From Space - That name alone makes it great but it is a very good Space Invaders clone.
Cosmic Ark - Shoot asteroids and abduct people, how can you go wrong ?
Dark Chambers - Closest thing to Gauntlet on the 2600.
Demon Attack - Probably the best Space Invaders clone similar to Phoenix but it's an Imagic game and looks great.
Dolphin - It's like Ecco the Dolphin only it's on the 2600.
Dragonfire - Steal treasure from a dragon, nothing else needs to be said.
DragonStomper - Insane RPG game for its time, try it out.
Enduro - Awesome racing game, Outrun before Outrun.
Frostbite - Mix of Q-Bert meets Frogger but with a unique twist, fun game.
H.E.R.O - It's freaking H.E.R.O. arguably the best game on the system.
Keystone Kapers - Fun game I played for many hours as a kid.
Laser Blast - Fun Space Invaders in reverse, you play the invader destroying the base.
Official Frogger - This was made by Starpath for the Super Charger addon. It looks great, you have to see it in comparison to the Parker Bros version.
Pac-Man (8K homebrew) - This one you need to get from Atariage forums. This is how Pac-Man should have been on the system.
Pengo - Fun puzzle game.
Phoenix - Space Invaders clone but I played it a lot as a kid so it's on here.
Pitfall and Pitfall II - 'Nuff said.
River Raid - Also 'nuff said, play it if you never played it.
Sea Quest - Fun underwater horizontal shooter.
Solaris - Late release for the system, looks great and is a lot of fun.
Space Rocks - This is another Atariage homebrew and is the best version of Asteroids on the 2600. The original Asteroids is left off because of this version.
Spider Fighter - Another Activision games and great fast paced shooter.
Stampede - Rope cows, how many games has this ? A lot of fun and played it a lot as a kid.
Starmaster - First person space combat and another Activision game.
Survival Island - Another Starpath Super Charger addon game, swim to the island without getting eaten.
Tutankham - Raid tombs and steal treasure.
Yars Revenge - System exclusive and a classic.