You can see what animal or thing a pokemon is based off of, as well as an origin for its name by going to bulbapedia and looking up that pokemon's profile...as for the "pikachu" like pokemon, there is:
Pikachu-obviously, and all the pokemon in its chain.
plusle/minun-the hoenn equivalent.
Pacharishu-The sinnoh version.
-please note that my answer doesn't include the B/W pokemon.