Formal:
* Presenter: This is the most common and neutral term.
* Speaker: This is used when the presentation is more focused on speaking and less on visuals.
* Lecturer: This is used in an academic context.
* Keynote speaker: This is used for a prominent speaker giving a major presentation.
Informal:
* Guy/gal giving the presentation: This is informal and casual.
* Person up front: This is informal and direct.
* The one who's talking: This is informal and humorous.
Specific:
* Salesperson: This is used if the presentation is a sales pitch.
* Professor/Teacher: This is used if the presentation is given by an educator.
* Expert: This is used if the person is presenting on a topic they have expertise in.
The best term to use depends on the specific situation and the tone you want to convey.