Formal:
* Speaker: This is the most general and formal term.
* Lecturer: Used for someone giving a formal presentation.
* Presenter: Similar to a lecturer, but could be in a more informal setting.
* Orator: Used for someone known for their eloquence and skill in public speaking.
* Narrator: Used for someone telling a story.
Informal:
* Talker: A general term for someone who speaks a lot.
* Chatterbox: Used for someone who talks constantly.
* Conversationalist: Someone who is good at holding a conversation.
* Voice: Used when referring to the person speaking, but focusing on their sound.
* Mouthpiece: Used to indicate someone speaking on behalf of someone else.
Other:
* The person speaking: A straightforward and neutral way to refer to them.
* They: Used if the person speaking is already known.
The best word to use will depend on the specific situation.