Formal:
* Soliloquy: A speech delivered by a character alone on stage, expressing their thoughts and feelings.
* Monologue: A long speech by one person, especially one delivered without interruption.
* Harangue: A lengthy and aggressive speech.
* Tirade: A long, angry speech.
Informal:
* Rant: A long, angry or excited speech.
* Diatribe: A bitter and abusive speech.
* Speachification: (Slang) A long, boring speech.
Other options:
* Address: A formal speech delivered to an audience.
* Lecture: A formal talk on a particular subject.
* Discourse: A long and formal discussion of a topic.
The best synonym for "monolog" will depend on the specific context and the tone you want to convey.