Red/Blue
Charmander as starter: Charizard, Dugtrio, Snorlax, Exeggutor, Fearow, Lapras
Charizard: Flamethrower, Fire Spin, Slash, Earthquake
-Your starter. While it needs some assistance against Brock and probably Misty (unless you grind like I do) it is still a powerful Pokemon, easily taking down Erika and using its powerful neutral hits against the other Gym Leaders. Flamethrower is your main STAB attack. While it isn't as powerful as Fire Blast, it has more PP, making it more useful for ingame. Fire Spin can just wear the opponent down to a point where you can easily KO them. It's a very deadly move in RBY. Slash gets that great critical hit chance, and is very helpful against Water type foes. Earthquake has high base power and is used to break through Rock types who resist Flamethrower and Slash.
Dugtrio: Earthquake, Slash, Rock Slide, Cut
-At the time you get Dugtrio, it might very well be a higher level than your starter Pokemon. It wasn't that case for me, but I grind. You also get it right as you are about to face the Electric type Gym Leader, so it just gives you a huge advantage. It helps out against Lt. Surge, Koga, Blaine, and Agatha. Earthquake is STAB. Slash is for crits. With its high speed stat, you'll be critting all the time. Rock Slide is coverage against Flying types. Cut is an HM. It has a small movepool, so you don't lose anything by using Cut.
Snorlax: Strength, Hyper Beam, Surf, Blizzard
-Feel free to use Tauros or Chansey if you get them. Chances are, you won't get them. Snorlax comes at a nice level and is incredibly powerful in its own right. Strength is an HM and gets STAB. It only has 5 less base power than Body Slam, which is the most powerful non-recoil more than 5 PP STAB attack Snorlax gets. Hyper Beam can take down pretty much any foe. Use it to KO. Surf is an HM that takes down Rock types. Blizzard is just additional coverage. I only used it against Lance though.
Exeggutor: Psychic, Mega Drain, Sleep Powder, Egg Bomb
-I used Alakazam on my latest ingame team, but since some people won't have access to trading, I replaced it here with Exeggutor. Giovanni, Bruno, and Agatha fall easily to Exeggutor. Psychic and Mega Drain are STAB. Sleep Powder puts foes to sleep, making them easier to beat or to catch depending on the situation. Egg Bomb is just an attack. Sparse movepool and all.
Fearow: Hyper Beam, Drill Peck, Fly, Mimic
-While not as good as Dodrio, it gets a massive level advantage due to be obtained so early on. Hyper Beam and Drill Peck are STAB. Fly is a very useful HM. Mimic can be used to nab something neat.
Lapras: Surf, Ice Beam, Thunderbolt, Psychic
-Helpful against Blaine and Giovanni, it is also your best bet against Lance. Surf and Ice Beam are STAB while Thunderbolt and Psychic are coverage.