From Bulbapedia, the community-driven Pokémon encyclopedia.
This is a list of Pokémon with unique type combinations across the generations. A Pokémon qualifies as having a unique type combination if no other Pokémon aside from any evolutionary relatives has that type combination. Since the game makes no distinction between a Pokémon's first and second types when calculating damage, this list does not consider every permutation of types, but instead considers only combinations. In other words, Pokémon such as Spiritomb (a Ghost/Dark-type Pokémon) and Sableye (a Dark/Ghost-type Pokémon) are treated as having the same type combination.
List of Pokémon with unique type combinations
List of Pokémon with formerly unique type combinations