Only in Pokémon Black, it is possible to catch Weedle, Kakuna, Beedrill, Murkrow, Houndour, Houndoom, Shroomish, Breloom, Plusle, Volbeat, Cottonee, Whimsicott, Gothita, Gothorita, Gothitelle, Vullaby, Mandibuzz, Tornadus, and Reshiram. Only in Pokémon White, it is possible to catch Caterpie, Metapod, Butterfree, Paras, Parasect, Misdreavus, Poochyena, Mightyena, Minum, Illumise, Petilil, Lilligant, Solosis, Duosion, Reuniclus, Rufflet, Braviary, Thundurus, and Zekrom. There are also certain aesthetic changes and specific battles that are different.
The Legendary Pokémon that joins the player to fight the mysterious "N" character is dependent on which game the player has. When playing Pokémon White, the player receives the black Electric- and Dragon-type Pokémon named Zekrom. When playing Pokémon Black, the player receives the white Fire- and Dragon-type Pokémon Reshiram.
The Legendary Weather Trio Pokémon that a player encounters also depend on which version of the game he plays. Players with Pokémon Black encounter Thundurus, while players with Pokémon White encounter Tornadus. Both of these Pokémon are needed to gain access to Landorus, so a player needs to trade across game versions in order to obtain them.
Besides the fact that each version has certain exclusive Pokémon, there are aesthetic differences between Opelucid City and Mistralton City. Drayden is the gym leader of Opelucid in Pokémon Black but in Pokémon White it is Iris.
Serebii explains that in Pokémon Black, there is an industrial area called Black City; but in Pokémon White, it is replaced by an area called White Forest. In Pokémon Black, the cities seem more advanced and futuristic. The buildings have neon lights, automatic doors, and greenhouses. In Pokémon White, the cities are more rural and traditional. The buildings have mossy stone paths, barns, and gardens.
According to Bulbapedia, in both games there is a character called Charles the heart breaker. In Pokémon Black, he challenges the player to a rotation battle; and, in Pokémon White, he challenges the player to a triple battle.