Formal:
* Bavard: This is the most common and neutral term. It simply means "talkative."
* Loquace: This word is a bit more formal and literary. It implies someone who speaks eloquently and fluently.
Informal:
* Caquet: This is a more informal term, often used to describe someone who talks incessantly and perhaps even gossips.
* Pipelette: This word is specifically used for a woman who talks a lot, and it can have a slightly negative connotation.
* Parlotte: Similar to "pipelette," this term is also used for women who talk a lot, but it can also be used playfully.
Other options:
* Un moulin à paroles: This literally means "a word mill" and is a more poetic way to describe a chatterbox.
* Un bavardage: This word refers to the act of chattering or talking excessively.
The best way to choose the right word depends on the specific situation and your desired level of formality.