A study has done since 2010 on Sporcle to determine which Pokemon is the most memorable from the first games. It was determined when the study started that Pikachu was ranked the highest, but more recently Charmander and Bulbasaur have pushed Pikachu down. According to their chart, they rose pretty quickly and have maintained their rankings since 2012. It’s interesting to point out that the electric mouse continues to fall despite being recognized as the series icon. In case you were wondering which other two Pokemon outrank poor Pikachu, they are Charizard and Squirtle.
Sporcle believes their popularity is maintained along with seeing Pikachu drop further from Google Trends. 2013 saw Charmander, Bulbasaur and Squirtle return as the starter Pokemon for Pokemon X and Pokemon Y. They also have the full list on their site, which includes the least memorable Lickitung.