OK, so I started this run a little while ago, so I'll just make this a playthrough thread. Again, I'm restricting myself to Pokes that are NOT single-stage (Jynx, Pinsir, Tauros, etc.) and are first-stage only.
I started with Bulbasaur, my favorite starter across all the games. Smart money would've taken Squirtle to solve my Ice Beam/Blizzard problem, but I'm going to pick up Horsea for that later on. I'm super familiar with the Bulbasaur line, with Venusaur being my favorite Pokemon overall. I also figured that while Exeggcute would do a better job in most other departments, I won't be getting it until late in the game and thus the stat experience won't be there. Plus the slower EXP growth in general and limited number of trainers from that point on.
Anywho, once I got to Viridian Forest I picked up a Pikachu. I didn't want to use Pikachu initially, but I'm very comfortable with Pikachu/Raichu so I decided to go with it. Though I have a feeling this guy is going to not be so useful against the Elite 4 aside from being my fastest Thunder Wave user. We shall see.
I was going to pick up a Rhyhorn due to it's great stats for a first stage Pokemon, but like I said in my paragraph about Bulbasaur, the stat experience won't be there. So I picked up a Geodude in Mt. Moon. This guy has been amazing so far. Been working out really well with some Thunder Wave setup.
I had very few issues until I got past Misty's gym. It's still not real difficult, but the lack of power from the evolved forms is becoming noticeable. I'm currently outside of Vermillion City trying to catch a Drowzee. That guy will serve as my backup Thunder Wave user & general OP Psychic type. Very solid base stats too, including a base 90 for a Special stat.
The other two Pokemon I'm going to pick up are Gastly & Horsea. Gastly is pretty self-explanatory. It's just darn good. Horsea... I had to really think about that one. There are no first stage ice types to really take advantage of STAB Ice Beam/Blizzard. All the ice types in RBY are either single-stage (Jynx, Articuno, Lapras) or evolved forms (Dewgong, Cloyster). I narrowed it down to Poliwag, Staryu or Horsea. I liked Poliwag's base speed (90), but since critical hits are determined by the base speed stat and crit damage is not affected by stat buffs/debuffs in RBY I figured I won't get the mileage out of Amnesia that I want. I liked Staryu for it's base stats and fantastic moveset. But I noticed that Staryu falls victim to 5 moveslot syndrome, and most of the moves and recovery it gets I can use other Pokes and items for. While Minimize is useful, it doesn't affect the opposing Pokemon (who is not likely to ever switch), which makes Smokescreen the better pick for me. Smokescreen, slightly better defensive stats and a good special stat got me to pick Horsea.
So, going into the area around Vermillion City I'll have Bulbasaur, Pikachu, Geodude & Drowzee. I'll pick up Gastly & Horsea later on. Geodude will be my star in the gym, but I'm anticipating this playthrough to be a bit slower than previous ones.