Gen 5 really is a chore to replay, especially at the start.
Pokemon you can catch before the first gym:
>Patrat and Lillipup

Meanwhile, Kanto
>Rattata, Pidgey, Spearow, Mankey, Pikachu, Caterpie, Weedle

Johto
>Sentret, Caterpie, Weedle, Pidgey, Hoothoot, Bellsprout, Geodude

Hoenn
>Poochyena, Zigzagoon, Lotad, Seedot, Wingull, Taillow, Wurmple, Shroomish, Nincada, Whismur, Slakoth, Ralts, Magikarp

So on
Unova lacks variety at the start, at least in BW. Most of the cooler mons are locked till mid or endgame