Formal:
* À plus tard! (Ah ploo tahr) - This is the most common and versatile phrase, suitable for most situations.
* On se retrouve plus tard. (On seh ruh-troov pluh tahr) - This means "We will meet again later."
Informal:
* À tout à l'heure! (Ah too tah loohr) - This literally means "Until later" and is very common among friends.
* On se voit plus tard! (On seh vwa pluh tahr) - This means "See you later!" and is more casual than "On se retrouve plus tard."
* Ciao! - This is a more informal Italian word, but it's also used in French as a way to say goodbye, particularly among young people.
More specific:
* À demain! (Ah duh-man) - This means "Until tomorrow."
* À ce soir! (Ah seh swar) - This means "Until tonight."
The best way to choose the right phrase is to consider your relationship with the person you're talking to and the situation.