Formal:
* En effet: This is the most common and formal translation.
* Effectivement: This is also formal and emphasizes the truthfulness of the statement.
Informal:
* En fait: This is more casual and means "in fact" or "actually."
* En vérité: This is a bit more poetic and means "in truth."
* C'est ça: This is very informal and means "that's right."
Other options:
* Bien sûr: This is a more emphatic way of saying "indeed" and means "of course."
* Sans aucun doute: This translates to "without any doubt" and implies certainty.
The best translation will depend on the specific situation. If you are unsure, it's best to stick with "en effet" as it is the most widely understood and accepted.