Formal:
* Teachers (the most common and straightforward)
* Faculty (if you are referring to a group of teachers in a school or institution)
* Instructors (a more general term for someone who teaches)
* Pedagogues (a more formal term for someone who teaches)
Informal:
* A bunch of teachers
* Lots of teachers
* Several teachers
You can also use plural possessive forms:
* The teachers' lounge
* The teachers' desks
The best term to use will depend on the specific situation.