Get a Mankey. It will learn Low Kick at level 8. You can catch one left of Viridian City, in the grass before you fight you Rival a second (but optional) time. It is the first patch of grass on the way to the PKMN league. Mankey evolves into a powerful Primeape. Also Xbox_gamer's idea is good too, but Butterfree isn't the kind of PKMN you want to train the entire game. It is weak against many types and cannot learn very many powerful moves by itself in it's early levels. Even at level 58 it is still too weak.
RAWR! Who's the Boogie Monster NOW!!! MUHAHAHA