General:
* Speak
* Converse
* Chat
* Discuss
* Communicate
* Confer
* Dialogue
* Exchange
* Speak to
* Have a conversation
Informal:
* Shoot the breeze
* Gab
* Jaw
* Rap
* Yack
Formal:
* Discourse
* Elocution
* Oratory
* Harangue (usually refers to a long and aggressive speech)
Specific situations:
* Negotiate (talking to reach an agreement)
* Argue (talking to express disagreement)
* Explain (talking to make something clear)
* Persuade (talking to convince someone)
The best synonym for "talk" will depend on the specific situation and the intended meaning.