Black (the one I have):
Black City - Here you can get rare items and battle others.
Reshiram - The white legendary pokemon.
Opelucid City - In Opelucid City gym you battle Drayden.
White:
White Forest - Here you can catch rare pokemon.
Zekrom - The black legendary pokemon.
Opelucid City - In Opelucid City gym you battle Iris.