Formal:
* Presenting
* Delivering a speech
* Addressing an audience
* Giving a lecture
* Making a presentation
Informal:
* Talking to a group
* Giving a talk
* Public speaking
* Performing (if it's more of a show)
* Sharing (if it's more casual)
Specific:
* Debating (if you are arguing a point)
* Orating (if it's a formal, eloquent speech)
* Preaching (if it's a religious address)
* Advocating (if you are promoting a cause)
The best word to use will depend on the specific situation.