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Charizard, Jigglypuff, Squirtle, Blastoise and Mewtwo seem to be the most popular besides Pikachu.
I don't see quite as much Charmander and certainly not as much Bulbasaur, but I'm sure they're not far behind. Eevee is popular in-fandom but not well known outside of that. Meowth might also be pretty well known due to being in the show so much.
I don't really know how well-known any Pokemon from other generations are outside of the core fanbase. I'd wager it's Pokemon like Piplup, Oshawott, etc. that appear in the anime for a few years and are known to parents who have their kids watching Pokemon, but then their popularity dies down after each series starring them is over.
