More formal:
* Coterie: A small, exclusive group of people with shared interests.
* Clique: A small, exclusive group of people, often with a negative connotation.
* Cabal: A secret political group or faction.
* Party: This can refer to a formal political party, or to a smaller group within a party.
* Bloc: A group of people or countries with shared interests.
More informal:
* Camp: A group of people with similar opinions or beliefs.
* Wing: A group within a larger organization with a specific set of views.
* Circle: A group of people with a common interest or purpose.
* Group: A general term for any collection of people.
The best word to use will depend on the specific context.